Bacteriochlorophylls: Pyrrole containing pigments found in photosynthetic bacteria.Bacteriochlorophyll A: A specific bacteriochlorophyll that is similar in structure to chlorophyll a.Chlorobi: A phylum of anoxygenic, phototrophic bacteria including the family Chlorobiaceae. They occur in aquatic sediments, sulfur springs, and hot springs and utilize reduced sulfur compounds instead of oxygen.Rhodopseudomonas: A genus of gram-negative, rod-shaped, phototrophic bacteria found in aquatic environments. Internal photosynthetic membranes are present as lamellae underlying the cytoplasmic membrane.Bacterial Chromatophores: Organelles of phototrophic bacteria which contain photosynthetic pigments and which are formed from an invagination of the cytoplasmic membrane.Rhodobacter sphaeroides: Spherical phototrophic bacteria found in mud and stagnant water exposed to light.Chlorobium: A genus of phototrophic, obligately anaerobic bacteria in the family Chlorobiaceae. They are found in hydrogen sulfide-containing mud and water environments.Light-Harvesting Protein Complexes: Complexes containing CHLOROPHYLL and other photosensitive molecules. They serve to capture energy in the form of PHOTONS and are generally found as components of the PHOTOSYSTEM I PROTEIN COMPLEX or the PHOTOSYSTEM II PROTEIN COMPLEX.Chlorophyll: Porphyrin derivatives containing magnesium that act to convert light energy in photosynthetic organisms.Rhodospirillum: A genus of gram-negative, spiral bacteria that possesses internal photosynthetic membranes. Its organisms divide by binary fission, are motile by means of polar flagella, and are found in aquatic environments.Photosynthetic Reaction Center Complex Proteins: Protein complexes that take part in the process of PHOTOSYNTHESIS. They are located within the THYLAKOID MEMBRANES of plant CHLOROPLASTS and a variety of structures in more primitive organisms. There are two major complexes involved in the photosynthetic process called PHOTOSYSTEM I and PHOTOSYSTEM II.Rhodospirillales: An order of photosynthetic bacteria representing a physiological community of predominantly aquatic bacteria.Rhodobacter capsulatus: Non-pathogenic ovoid to rod-shaped bacteria that are widely distributed and found in fresh water as well as marine and hypersaline habitats.Photosynthesis: The synthesis by organisms of organic chemical compounds, especially carbohydrates, from carbon dioxide using energy obtained from light rather than from the oxidation of chemical compounds. Photosynthesis comprises two separate processes: the light reactions and the dark reactions. In higher plants; GREEN ALGAE; and CYANOBACTERIA; NADPH and ATP formed by the light reactions drive the dark reactions which result in the fixation of carbon dioxide. (from Oxford Dictionary of Biochemistry and Molecular Biology, 2001)Rhodospirillum rubrum: Vibrio- to spiral-shaped phototrophic bacteria found in stagnant water and mud exposed to light.Carotenoids: The general name for a group of fat-soluble pigments found in green, yellow, and leafy vegetables, and yellow fruits. They are aliphatic hydrocarbons consisting of a polyisoprene backbone.Chromatium: A genus of gram-negative, ovoid to rod-shaped bacteria that is phototrophic. All species use ammonia as a nitrogen source. Some strains are found only in sulfide-containing freshwater habitats exposed to light while others may occur in marine, estuarine, and freshwater environments.Phototrophic Processes: Processes by which phototrophic organisms use sunlight as their primary energy source. Contrasts with chemotrophic processes which do not depend on light and function in deriving energy from exogenous chemical sources. Photoautotrophy (or photolithotrophy) is the ability to use sunlight as energy to fix inorganic nutrients to be used for other organic requirements. Photoautotrophs include all GREEN PLANTS; GREEN ALGAE; CYANOBACTERIA; and green and PURPLE SULFUR BACTERIA. Photoheterotrophs or photoorganotrophs require a supply of organic nutrients for their organic requirements but use sunlight as their primary energy source; examples include certain PURPLE NONSULFUR BACTERIA. Depending on environmental conditions some organisms can switch between different nutritional modes (AUTOTROPHY; HETEROTROPHY; chemotrophy; or phototrophy) to utilize different sources to meet their nutrients and energy requirements.Alphaproteobacteria: A class in the phylum PROTEOBACTERIA comprised mostly of two major phenotypes: purple non-sulfur bacteria and aerobic bacteriochlorophyll-containing bacteria.Pheophytins: Chlorophylls from which the magnesium has been removed by treatment with weak acid.Pigments, Biological: Any normal or abnormal coloring matter in PLANTS; ANIMALS or micro-organisms.Aerobiosis: Life or metabolic reactions occurring in an environment containing oxygen.Rhodospirillaceae: A family of phototrophic bacteria, in the order Rhodospirillales, isolated from stagnant water and mud.Chromatiaceae: A family of phototrophic purple sulfur bacteria that deposit globules of elemental sulfur inside their cells. They are found in diverse aquatic environments.Rhodobacter: A genus of gram-negative bacteria widely distributed in fresh water as well as marine and hypersaline habitats.Levulinic Acids: Keto acids that are derivatives of 4-oxopentanoic acids (levulinic acid).Light: That portion of the electromagnetic spectrum in the visible, ultraviolet, and infrared range.Bacterial Proteins: Proteins found in any species of bacterium.Tetrapyrroles: Four PYRROLES joined by one-carbon units linking position 2 of one to position 5 of the next. The conjugated bond system results in PIGMENTATION.Azaguanine: One of the early purine analogs showing antineoplastic activity. It functions as an antimetabolite and is easily incorporated into ribonucleic acids.Rhodobacteraceae: A family in the order Rhodobacterales, class ALPHAPROTEOBACTERIA.RNA, Ribosomal, 16S: Constituent of 30S subunit prokaryotic ribosomes containing 1600 nucleotides and 21 proteins. 16S rRNA is involved in initiation of polypeptide synthesis.Energy Transfer: The transfer of energy of a given form among different scales of motion. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed). It includes the transfer of kinetic energy and the transfer of chemical energy. The transfer of chemical energy from one molecule to another depends on proximity of molecules so it is often used as in techniques to measure distance such as the use of FORSTER RESONANCE ENERGY TRANSFER.DNA, Ribosomal: DNA sequences encoding RIBOSOMAL RNA and the segments of DNA separating the individual ribosomal RNA genes, referred to as RIBOSOMAL SPACER DNA.Chromatophores: The large pigment cells of fish, amphibia, reptiles and many invertebrates which actively disperse and aggregate their pigment granules. These cells include MELANOPHORES, erythrophores, xanthophores, leucophores and iridiophores. (In algae, chromatophores refer to CHLOROPLASTS. In phototrophic bacteria chromatophores refer to membranous organelles (BACTERIAL CHROMATOPHORES).)Aminolevulinic Acid: A compound produced from succinyl-CoA and GLYCINE as an intermediate in heme synthesis. It is used as a PHOTOCHEMOTHERAPY for actinic KERATOSIS.Spectrophotometry: The art or process of comparing photometrically the relative intensities of the light in different parts of the spectrum.Spectrum Analysis: The measurement of the amplitude of the components of a complex waveform throughout the frequency range of the waveform. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Seawater: The salinated water of OCEANS AND SEAS that provides habitat for marine organisms.Roseobacter: A genus of obligately aerobic marine phototrophic and chemoorganotrophic bacteria, in the family RHODOBACTERACEAE.Bacteria, AerobicPhylogeny: The relationships of groups of organisms as reflected by their genetic makeup.Chlorophyllides: Products of the hydrolysis of chlorophylls in which the phytic acid side chain has been removed and the carboxylic acids saponified.North SeaSphingomonadaceae: A family of gram-negative, asporogenous rods or ovoid cells, aerobic or facultative anaerobic chemoorganotrophs. They are commonly isolated from SOIL, activated sludge, or marine environments.Heterotrophic Processes: The processes by which organisms utilize organic substances as their nutrient sources. Contrasts with AUTOTROPHIC PROCESSES which make use of simple inorganic substances as the nutrient supply source. Heterotrophs can be either chemoheterotrophs (or chemoorganotrophs) which also require organic substances such as glucose for their primary metabolic energy requirements, or photoheterotrophs (or photoorganotrophs) which derive their primary energy requirements from light. Depending on environmental conditions some organisms can switch between different nutritional modes (AUTOTROPHY; heterotrophy; chemotrophy; or PHOTOTROPHY) to utilize different sources to meet their nutrients and energy requirements.Acetobacteraceae: A family of gram-negative aerobic bacteria consisting of ellipsoidal to rod-shaped cells that occur singly, in pairs, or in chains.Iron Isotopes: Stable iron atoms that have the same atomic number as the element iron, but differ in atomic weight. Fe-54, 57, and 58 are stable iron isotopes.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Carbon-Oxygen Ligases: Enzymes that catalyze the joining of two molecules by the formation of a carbon-oxygen bond. EC 6.1.PhytolGenes, rRNA: Genes, found in both prokaryotes and eukaryotes, which are transcribed to produce the RNA which is incorporated into RIBOSOMES. Prokaryotic rRNA genes are usually found in OPERONS dispersed throughout the GENOME, whereas eukaryotic rRNA genes are clustered, multicistronic transcriptional units.Ectothiorhodospira: A genus of vibrioid or rod-shaped cells which are motile by polar flagella. Internal photosynthetic membranes are present as lamellar stacks and contain bacteriochlorophyll a or b and carotenoids. Growth occurs photoautotrophically under anaerobic conditions. (From Bergey's Manual of Determinative Bacteriology, 9th ed)Base Composition: The relative amounts of the PURINES and PYRIMIDINES in a nucleic acid.Spectrophotometry, Infrared: Spectrophotometry in the infrared region, usually for the purpose of chemical analysis through measurement of absorption spectra associated with rotational and vibrational energy levels of molecules. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Oxygen Isotopes: Stable oxygen atoms that have the same atomic number as the element oxygen, but differ in atomic weight. O-17 and 18 are stable oxygen isotopes.Porphyrins: A group of compounds containing the porphin structure, four pyrrole rings connected by methine bridges in a cyclic configuration to which a variety of side chains are attached. The nature of the side chain is indicated by a prefix, as uroporphyrin, hematoporphyrin, etc. The porphyrins, in combination with iron, form the heme component in biologically significant compounds such as hemoglobin and myoglobin.DNA, Bacterial: Deoxyribonucleic acid that makes up the genetic material of bacteria.Rhodovulum: A genus of facultatively or obligately anaerobic marine phototrophic bacteria, in the family RHODOBACTERACEAE.Acidobacteria: A physiologically diverse phylum of acidophilic, gram-negative bacteria found in a wide variety of habitats, but particularly abundant in soils and sediments.Bacteria: One of the three domains of life (the others being Eukarya and ARCHAEA), also called Eubacteria. They are unicellular prokaryotic microorganisms which generally possess rigid cell walls, multiply by cell division, and exhibit three principal forms: round or coccal, rodlike or bacillary, and spiral or spirochetal. Bacteria can be classified by their response to OXYGEN: aerobic, anaerobic, or facultatively anaerobic; by the mode by which they obtain their energy: chemotrophy (via chemical reaction) or PHOTOTROPHY (via light reaction); for chemotrophs by their source of chemical energy: CHEMOLITHOTROPHY (from inorganic compounds) or chemoorganotrophy (from organic compounds); and by their source for CARBON; NITROGEN; etc.; HETEROTROPHY (from organic sources) or AUTOTROPHY (from CARBON DIOXIDE). They can also be classified by whether or not they stain (based on the structure of their CELL WALLS) with CRYSTAL VIOLET dye: gram-negative or gram-positive.Proteobacteria: A phylum of bacteria consisting of the purple bacteria and their relatives which form a branch of the eubacterial tree. This group of predominantly gram-negative bacteria is classified based on homology of equivalent nucleotide sequences of 16S ribosomal RNA or by hybridization of ribosomal RNA or DNA with 16S and 23S ribosomal RNA.Chloroflexus: A genus of green nonsulfur bacteria in the family Chloroflexaceae. They are photosynthetic, thermophilic, filamentous gliding bacteria found in hot springs.Phycobiliproteins: Light harvesting proteins found in phycobilisomes.Electron Transport: The process by which ELECTRONS are transported from a reduced substrate to molecular OXYGEN. (From Bennington, Saunders Dictionary and Encyclopedia of Laboratory Medicine and Technology, 1984, p270)Genes, Bacterial: The functional hereditary units of BACTERIA.RNA, Bacterial: Ribonucleic acid in bacteria having regulatory and catalytic roles as well as involvement in protein synthesis.Water Microbiology: The presence of bacteria, viruses, and fungi in water. This term is not restricted to pathogenic organisms.Sequence Analysis, DNA: A multistage process that includes cloning, physical mapping, subcloning, determination of the DNA SEQUENCE, and information analysis.Protochlorophyllide: A photo-active pigment localized in prolamellar bodies occurring within the proplastids of dark-grown bean leaves. In the process of photoconversion, the highly fluorescent protochlorophyllide is converted to chlorophyll.Organelles: Specific particles of membrane-bound organized living substances present in eukaryotic cells, such as the MITOCHONDRIA; the GOLGI APPARATUS; ENDOPLASMIC RETICULUM; LYSOSOMES; PLASTIDS; and VACUOLES.Oxidoreductases Acting on CH-CH Group Donors: A subclass of enzymes which includes all dehydrogenases acting on carbon-carbon bonds. This enzyme group includes all the enzymes that introduce double bonds into substrates by direct dehydrogenation of carbon-carbon single bonds.Oxygen: An element with atomic symbol O, atomic number 8, and atomic weight [15.99903; 15.99977]. It is the most abundant element on earth and essential for respiration.Quinones: Hydrocarbon rings which contain two ketone moieties in any position. They can be substituted in any position except at the ketone groups.PhotochemistryOxidoreductases: The class of all enzymes catalyzing oxidoreduction reactions. The substrate that is oxidized is regarded as a hydrogen donor. The systematic name is based on donor:acceptor oxidoreductase. The recommended name will be dehydrogenase, wherever this is possible; as an alternative, reductase can be used. Oxidase is only used in cases where O2 is the acceptor. (Enzyme Nomenclature, 1992, p9)Darkness: The absence of light.Gram-Negative Aerobic Bacteria: A large group of aerobic bacteria which show up as pink (negative) when treated by the gram-staining method. This is because the cell walls of gram-negative bacteria are low in peptidoglycan and thus have low affinity for violet stain and high affinity for the pink dye safranine.Gammaproteobacteria: A group of the proteobacteria comprised of facultatively anaerobic and fermentative gram-negative bacteria.Fresh Water: Water containing no significant amounts of salts, such as water from RIVERS and LAKES.Thiosulfates: Inorganic salts of thiosulfuric acid possessing the general formula R2S2O3.Anaerobiosis: The complete absence, or (loosely) the paucity, of gaseous or dissolved elemental oxygen in a given place or environment. (From Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)Secale cereale: A hardy grain crop, rye, grown in northern climates. It is the most frequent host to ergot (CLAVICEPS), the toxic fungus. Its hybrid with TRITICUM is TRITICALE, another grain.Lyases: A class of enzymes that catalyze the cleavage of C-C, C-O, and C-N, and other bonds by other means than by hydrolysis or oxidation. (Enzyme Nomenclature, 1992) EC 4.Geologic Sediments: A mass of organic or inorganic solid fragmented material, or the solid fragment itself, that comes from the weathering of rock and is carried by, suspended in, or dropped by air, water, or ice. It refers also to a mass that is accumulated by any other natural agent and that forms in layers on the earth's surface, such as sand, gravel, silt, mud, fill, or loess. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed, p1689)Hyphomicrobiaceae: A family in the order Rhizobiales, class ALPHAPROTEOBACTERIA comprised of many genera of budding or appendaged bacteria.Oxidation-Reduction: A chemical reaction in which an electron is transferred from one molecule to another. The electron-donating molecule is the reducing agent or reductant; the electron-accepting molecule is the oxidizing agent or oxidant. Reducing and oxidizing agents function as conjugate reductant-oxidant pairs or redox pairs (Lehninger, Principles of Biochemistry, 1982, p471).Sodium Chloride: A ubiquitous sodium salt that is commonly used to season food.Fatty Acids: Organic, monobasic acids derived from hydrocarbons by the equivalent of oxidation of a methyl group to an alcohol, aldehyde, and then acid. Fatty acids are saturated and unsaturated (FATTY ACIDS, UNSATURATED). (Grant & Hackh's Chemical Dictionary, 5th ed)Bacterial Typing Techniques: Procedures for identifying types and strains of bacteria. The most frequently employed typing systems are BACTERIOPHAGE TYPING and SEROTYPING as well as bacteriocin typing and biotyping.Spectrometry, Fluorescence: Measurement of the intensity and quality of fluorescence.Mutation: Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.Microscopy, Electron: Microscopy using an electron beam, instead of light, to visualize the sample, thereby allowing much greater magnification. The interactions of ELECTRONS with specimens are used to provide information about the fine structure of that specimen. In TRANSMISSION ELECTRON MICROSCOPY the reactions of the electrons that are transmitted through the specimen are imaged. In SCANNING ELECTRON MICROSCOPY an electron beam falls at a non-normal angle on the specimen and the image is derived from the reactions occurring above the plane of the specimen.Puromycin: A cinnamamido ADENOSINE found in STREPTOMYCES alboniger. It inhibits protein synthesis by binding to RNA. It is an antineoplastic and antitrypanosomal agent and is used in research as an inhibitor of protein synthesis.Spectrum Analysis, Raman: Analysis of the intensity of Raman scattering of monochromatic light as a function of frequency of the scattered light.Sulfur: An element that is a member of the chalcogen family. It has an atomic symbol S, atomic number 16, and atomic weight [32.059; 32.076]. It is found in the amino acids cysteine and methionine.Circular Dichroism: A change from planar to elliptic polarization when an initially plane-polarized light wave traverses an optically active medium. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Temperature: The property of objects that determines the direction of heat flow when they are placed in direct thermal contact. The temperature is the energy of microscopic motions (vibrational and translational) of the particles of atoms.Cytochromes: Hemeproteins whose characteristic mode of action involves transfer of reducing equivalents which are associated with a reversible change in oxidation state of the prosthetic group. Formally, this redox change involves a single-electron, reversible equilibrium between the Fe(II) and Fe(III) states of the central iron atom (From Enzyme Nomenclature, 1992, p539). The various cytochrome subclasses are organized by the type of HEME and by the wavelength range of their reduced alpha-absorption bands.Protoporphyrins: Porphyrins with four methyl, two vinyl, and two propionic acid side chains attached to the pyrrole rings. Protoporphyrin IX occurs in hemoglobin, myoglobin, and most of the cytochromes.Kinetics: The rate dynamics in chemical or physical systems.Nitrogenase: An enzyme system that catalyzes the fixing of nitrogen in soil bacteria and blue-green algae (CYANOBACTERIA). EC 126.96.36.199.Freeze Fracturing: Preparation for electron microscopy of minute replicas of exposed surfaces of the cell which have been ruptured in the frozen state. The specimen is frozen, then cleaved under high vacuum at the same temperature. The exposed surface is shadowed with carbon and platinum and coated with carbon to obtain a carbon replica.Alcohols: Alkyl compounds containing a hydroxyl group. They are classified according to relation of the carbon atom: primary alcohols, R-CH2OH; secondary alcohols, R2-CHOH; tertiary alcohols, R3-COH. (From Grant & Hackh's Chemical Dictionary, 5th ed)Cyanobacteria: A phylum of oxygenic photosynthetic bacteria comprised of unicellular to multicellular bacteria possessing CHLOROPHYLL a and carrying out oxygenic PHOTOSYNTHESIS. Cyanobacteria are the only known organisms capable of fixing both CARBON DIOXIDE (in the presence of light) and NITROGEN. Cell morphology can include nitrogen-fixing heterocysts and/or resting cells called akinetes. Formerly called blue-green algae, cyanobacteria were traditionally treated as ALGAE.X-Ray Diffraction: The scattering of x-rays by matter, especially crystals, with accompanying variation in intensity due to interference effects. Analysis of the crystal structure of materials is performed by passing x-rays through them and registering the diffraction image of the rays (CRYSTALLOGRAPHY, X-RAY). (From McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Organoids: An organization of cells into an organ-like structure. Organoids can be generated in culture. They are also found in certain neoplasms.Models, Chemical: Theoretical representations that simulate the behavior or activity of chemical processes or phenomena; includes the use of mathematical equations, computers, and other electronic equipment.Operon: In bacteria, a group of metabolically related genes, with a common promoter, whose transcription into a single polycistronic MESSENGER RNA is under the control of an OPERATOR REGION.Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.Carbon: A nonmetallic element with atomic symbol C, atomic number 6, and atomic weight [12.0096; 12.0116]. It may occur as several different allotropes including DIAMOND; CHARCOAL; and GRAPHITE; and as SOOT from incompletely burned fuel.Sequence Homology, Nucleic Acid: The sequential correspondence of nucleotides in one nucleic acid molecule with those of another nucleic acid molecule. Sequence homology is an indication of the genetic relatedness of different organisms and gene function.Models, Molecular: Models used experimentally or theoretically to study molecular shape, electronic properties, or interactions; includes analogous molecules, computer-generated graphics, and mechanical structures.Amino Acid Sequence: The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.Gene Expression Regulation, Bacterial: Any of the processes by which cytoplasmic or intercellular factors influence the differential control of gene action in bacteria.Hydrogen Bonding: A low-energy attractive force between hydrogen and another element. It plays a major role in determining the properties of water, proteins, and other compounds.Methyltransferases: A subclass of enzymes of the transferase class that catalyze the transfer of a methyl group from one compound to another. (Dorland, 28th ed) EC 2.1.1.Species Specificity: The restriction of a characteristic behavior, anatomical structure or physical system, such as immune response; metabolic response, or gene or gene variant to the members of one species. It refers to that property which differentiates one species from another but it is also used for phylogenetic levels higher or lower than the species.Molecular Conformation: The characteristic three-dimensional shape of a molecule.Intracellular Membranes: Thin structures that encapsulate subcellular structures or ORGANELLES in EUKARYOTIC CELLS. They include a variety of membranes associated with the CELL NUCLEUS; the MITOCHONDRIA; the GOLGI APPARATUS; the ENDOPLASMIC RETICULUM; LYSOSOMES; PLASTIDS; and VACUOLES.Chromatography, High Pressure Liquid: Liquid chromatographic techniques which feature high inlet pressures, high sensitivity, and high speed.Carbon Isotopes: Stable carbon atoms that have the same atomic number as the element carbon, but differ in atomic weight. C-13 is a stable carbon isotope.Heme: The color-furnishing portion of hemoglobin. It is found free in tissues and as the prosthetic group in many hemeproteins.Ubiquinone: A lipid-soluble benzoquinone which is involved in ELECTRON TRANSPORT in mitochondrial preparations. The compound occurs in the majority of aerobic organisms, from bacteria to higher plants and animals.Soil Microbiology: The presence of bacteria, viruses, and fungi in the soil. This term is not restricted to pathogenic organisms.Protein Conformation: The characteristic 3-dimensional shape of a protein, including the secondary, supersecondary (motifs), tertiary (domains) and quaternary structure of the peptide chain. PROTEIN STRUCTURE, QUATERNARY describes the conformation assumed by multimeric proteins (aggregates of more than one polypeptide chain).Lasers: An optical source that emits photons in a coherent beam. Light Amplification by Stimulated Emission of Radiation (LASER) is brought about using devices that transform light of varying frequencies into a single intense, nearly nondivergent beam of monochromatic radiation. Lasers operate in the infrared, visible, ultraviolet, or X-ray regions of the spectrum.Fluorescence: The property of emitting radiation while being irradiated. The radiation emitted is usually of longer wavelength than that incident or absorbed, e.g., a substance can be irradiated with invisible radiation and emit visible light. X-ray fluorescence is used in diagnosis.Nucleic Acid Hybridization: Widely used technique which exploits the ability of complementary sequences in single-stranded DNAs or RNAs to pair with each other to form a double helix. Hybridization can take place between two complimentary DNA sequences, between a single-stranded DNA and a complementary RNA, or between two RNA sequences. The technique is used to detect and isolate specific sequences, measure homology, or define other characteristics of one or both strands. (Kendrew, Encyclopedia of Molecular Biology, 1994, p503)Microscopy, Electron, Transmission: Electron microscopy in which the ELECTRONS or their reaction products that pass down through the specimen are imaged below the plane of the specimen.Cell Membrane: The lipid- and protein-containing, selectively permeable membrane that surrounds the cytoplasm in prokaryotic and eukaryotic cells.Molecular Structure: The location of the atoms, groups or ions relative to one another in a molecule, as well as the number, type and location of covalent bonds.Spectrophotometry, Ultraviolet: Determination of the spectra of ultraviolet absorption by specific molecules in gases or liquids, for example Cl2, SO2, NO2, CS2, ozone, mercury vapor, and various unsaturated compounds. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Hydrogen-Ion Concentration: The normality of a solution with respect to HYDROGEN ions; H+. It is related to acidity measurements in most cases by pH = log 1/2[1/(H+)], where (H+) is the hydrogen ion concentration in gram equivalents per liter of solution. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Multigene Family: A set of genes descended by duplication and variation from some ancestral gene. Such genes may be clustered together on the same chromosome or dispersed on different chromosomes. Examples of multigene families include those that encode the hemoglobins, immunoglobulins, histocompatibility antigens, actins, tubulins, keratins, collagens, heat shock proteins, salivary glue proteins, chorion proteins, cuticle proteins, yolk proteins, and phaseolins, as well as histones, ribosomal RNA, and transfer RNA genes. The latter three are examples of reiterated genes, where hundreds of identical genes are present in a tandem array. (King & Stanfield, A Dictionary of Genetics, 4th ed)Phenotype: The outward appearance of the individual. It is the product of interactions between genes, and between the GENOTYPE and the environment.Electron Spin Resonance Spectroscopy: A technique applicable to the wide variety of substances which exhibit paramagnetism because of the magnetic moments of unpaired electrons. The spectra are useful for detection and identification, for determination of electron structure, for study of interactions between molecules, and for measurement of nuclear spins and moments. (From McGraw-Hill Encyclopedia of Science and Technology, 7th edition) Electron nuclear double resonance (ENDOR) spectroscopy is a variant of the technique which can give enhanced resolution. Electron spin resonance analysis can now be used in vivo, including imaging applications such as MAGNETIC RESONANCE IMAGING.