Aminopeptidases: A subclass of EXOPEPTIDASES that act on the free N terminus end of a polypeptide liberating a single amino acid residue. EC 3.4.11.Methionyl Aminopeptidases: Aminopeptidases that remove METHIONINE from the amino-terminus of a peptide chain, such as the initiator METHIONINE found on nascent peptide chains.Leucyl Aminopeptidase: A zinc containing enzyme of the hydrolase class that catalyzes the removal of the N-terminal amino acid from most L-peptides, particularly those with N-terminal leucine residues but not those with N-terminal lysine or arginine residues. This occurs in tissue cell cytosol, with high activity in the duodenum, liver, and kidney. The activity of this enzyme is commonly assayed using a leucine arylamide chromogenic substrate such as leucyl beta-naphthylamide.Glutamyl Aminopeptidase: A ZINC-dependent membrane-bound aminopeptidase that catalyzes the N-terminal peptide cleavage of GLUTAMATE (and to a lesser extent ASPARTATE). The enzyme appears to play a role in the catabolic pathway of the RENIN-ANGIOTENSIN SYSTEM.Antigens, CD13: Zinc-binding metalloproteases that are members of the type II integral membrane metalloproteases. They are expressed by GRANULOCYTES; MONOCYTES; and their precursors as well as by various non-hematopoietic cells. They release an N-terminal amino acid from a peptide, amide or arylamide.Cystinyl Aminopeptidase: A zinc-containing sialoglycoprotein that is used to study aminopeptidase activity in the pathogenesis of hypertension. EC and Tripeptidyl-Peptidases: A subclass of exopeptidases that includes enzymes which cleave either two or three AMINO ACIDS from the end of a peptide chain.Leucine: An essential branched-chain amino acid important for hemoglobin formation.Substrate Specificity: A characteristic feature of enzyme activity in relation to the kind of substrate on which the enzyme or catalytic molecule reacts.Dipeptidases: EXOPEPTIDASES that specifically act on dipeptides. EC 3.4.13.Protease Inhibitors: Compounds which inhibit or antagonize biosynthesis or actions of proteases (ENDOPEPTIDASES).Cathepsin C: A papain-like cysteine protease that has specificity for amino terminal dipeptides. The enzyme plays a role in the activation of several pro-inflammatory serine proteases by removal of their aminoterminal inhibitory dipeptides. Genetic mutations that cause loss of cathepsin C activity in humans are associated with PAPILLON-LEFEVRE DISEASE.Pyroglutamyl-Peptidase I: An enzyme that catalyzes the release of a N-terminal pyroglutamyl group from a polypeptide provided the next residue is not proline. It is inhibited by thiol-blocking reagents and occurs in mammalian tissues, microorganisms, and plants. (From Enzyme Nomenclature, 1992) EC 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.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.Peptide Hydrolases: Hydrolases that specifically cleave the peptide bonds found in PROTEINS and PEPTIDES. Examples of sub-subclasses for this group include EXOPEPTIDASES and ENDOPEPTIDASES.Metalloproteases: Proteases which use a metal, normally ZINC, in the catalytic mechanism. This group of enzymes is inactivated by metal CHELATORS.Hydrolysis: The process of cleaving a chemical compound by the addition of a molecule of water.Enkephalin, Leucine: One of the endogenous pentapeptides with morphine-like activity. It differs from MET-ENKEPHALIN in the LEUCINE at position 5. Its first four amino acid sequence is identical to the tetrapeptide sequence at the N-terminal of BETA-ENDORPHIN.Digestive System: A group of organs stretching from the MOUTH to the ANUS, serving to breakdown foods, assimilate nutrients, and eliminate waste. In humans, the digestive system includes the GASTROINTESTINAL TRACT and the accessory glands (LIVER; BILIARY TRACT; PANCREAS).Aeromonas: A genus of gram-negative, facultatively anaerobic, rod-shaped bacteria that occurs singly, in pairs, or in short chains. Its organisms are found in fresh water and sewage and are pathogenic to humans, frogs, and fish.Neprilysin: Enzyme that is a major constituent of kidney brush-border membranes and is also present to a lesser degree in the brain and other tissues. It preferentially catalyzes cleavage at the amino group of hydrophobic residues of the B-chain of insulin as well as opioid peptides and other biologically active peptides. The enzyme is inhibited primarily by EDTA, phosphoramidon, and thiorphan and is reactivated by zinc. Neprilysin is identical to common acute lymphoblastic leukemia antigen (CALLA Antigen), an important marker in the diagnosis of human acute lymphocytic leukemia. There is no relationship with CALLA PLANT.Endopeptidases: A subclass of PEPTIDE HYDROLASES that catalyze the internal cleavage of PEPTIDES or PROTEINS.Dipeptidyl Peptidase 4: A serine protease that catalyses the release of an N-terminal dipeptide. Several biologically-active peptides have been identified as dipeptidyl peptidase 4 substrates including INCRETINS; NEUROPEPTIDES; and CHEMOKINES. The protein is also found bound to ADENOSINE DEAMINASE on the T-CELL surface and is believed to play a role in T-cell activation.Dipeptides: Peptides composed of two amino acid units.Microvilli: Minute projections of cell membranes which greatly increase the surface area of the cell.Lepidoptera: A large order of insects comprising the butterflies and moths.Peptides: Members of the class of compounds composed of AMINO ACIDS joined together by peptide bonds between adjacent amino acids into linear, branched or cyclical structures. OLIGOPEPTIDES are composed of approximately 2-12 amino acids. Polypeptides are composed of approximately 13 or more amino acids. PROTEINS are linear polypeptides that are normally synthesized on RIBOSOMES.Oligopeptides: Peptides composed of between two and twelve amino acids.Hemolysin Proteins: Proteins from BACTERIA and FUNGI that are soluble enough to be secreted to target ERYTHROCYTES and insert into the membrane to form beta-barrel pores. Biosynthesis may be regulated by HEMOLYSIN FACTORS.Antigen Presentation: The process by which antigen is presented to lymphocytes in a form they can recognize. This is performed by antigen presenting cells (APCs). Some antigens require processing before they can be recognized. Antigen processing consists of ingestion and partial digestion of the antigen by the APC, followed by presentation of fragments on the cell surface. (From Rosen et al., Dictionary of Immunology, 1989)Amino Acids: Organic compounds that generally contain an amino (-NH2) and a carboxyl (-COOH) group. Twenty alpha-amino acids are the subunits which are polymerized to form proteins.Metals: Electropositive chemical elements characterized by ductility, malleability, luster, and conductance of heat and electricity. They can replace the hydrogen of an acid and form bases with hydroxyl radicals. (Grant & Hackh's Chemical Dictionary, 5th ed)Cloning, Molecular: The insertion of recombinant DNA molecules from prokaryotic and/or eukaryotic sources into a replicating vehicle, such as a plasmid or virus vector, and the introduction of the resultant hybrid molecules into recipient cells without altering the viability of those cells.Drug Design: The molecular designing of drugs for specific purposes (such as DNA-binding, enzyme inhibition, anti-cancer efficacy, etc.) based on knowledge of molecular properties such as activity of functional groups, molecular geometry, and electronic structure, and also on information cataloged on analogous molecules. Drug design is generally computer-assisted molecular modeling and does not include pharmacokinetics, dosage analysis, or drug administration analysis.Kinetics: The rate dynamics in chemical or physical systems.Sequence Alignment: The arrangement of two or more amino acid or base sequences from an organism or organisms in such a way as to align areas of the sequences sharing common properties. The degree of relatedness or homology between the sequences is predicted computationally or statistically based on weights assigned to the elements aligned between the sequences. This in turn can serve as a potential indicator of the genetic relatedness between the organisms.Endotoxins: Toxins closely associated with the living cytoplasm or cell wall of certain microorganisms, which do not readily diffuse into the culture medium, but are released upon lysis of the cells.Zinc: A metallic element of atomic number 30 and atomic weight 65.38. It is a necessary trace element in the diet, forming an essential part of many enzymes, and playing an important role in protein synthesis and in cell division. Zinc deficiency is associated with ANEMIA, short stature, HYPOGONADISM, impaired WOUND HEALING, and geophagia. It is known by the symbol Zn.Bacterial Proteins: Proteins found in any species of bacterium.Histocompatibility Antigens Class I: Membrane glycoproteins consisting of an alpha subunit and a BETA 2-MICROGLOBULIN beta subunit. In humans, highly polymorphic genes on CHROMOSOME 6 encode the alpha subunits of class I antigens and play an important role in determining the serological specificity of the surface antigen. Class I antigens are found on most nucleated cells and are generally detected by their reactivity with alloantisera. These antigens are recognized during GRAFT REJECTION and restrict cell-mediated lysis of virus-infected cells.Cations, Divalent: Positively charged atoms, radicals or groups of atoms with a valence of plus 2, which travel to the cathode or negative pole during electrolysis.Binding Sites: The parts of a macromolecule that directly participate in its specific combination with another molecule.Models, Molecular: Models used experimentally or theoretically to study molecular shape, electronic properties, or interactions; includes analogous molecules, computer-generated graphics, and mechanical structures.Metalloendopeptidases: ENDOPEPTIDASES which use a metal such as ZINC in the catalytic mechanism.Sequence Homology, Amino Acid: The degree of similarity between sequences of amino acids. This information is useful for the analyzing genetic relatedness of proteins and species.Cytosol: Intracellular fluid from the cytoplasm after removal of ORGANELLES and other insoluble cytoplasmic components.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)