Prokaryotic triterpenoids. The hopanoids of the purple non-sulphur bacterium Rhodomicrobium vannielii: an aminotriol and its aminoacyl derivatives, N-tryptophanyl and N-ornithinyl aminotriol.
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Triterpenoids belonging to the hopane family are widely distributed in prokaryotes. Three new hopanoids have now been isolated from the purple non-sulphur bacterium Rhodomicrobium vannielii and identified essentially by spectroscopic methods. The basic compound is the 35-aminobacteriohopane-32,33,34-triol, from which the other two hopanoids are derived by introduction of a tryptophanyl or an ornithinyl moiety linked to the amino group at C-35 via an amide linkage. This is the first report of hopanoids possessing an amino group in their side-chain and linked to aminoacyl residues. (+info)
Biological activities of lipopolysaccharides and lipid A from Rhodospirillaceae.
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The lipopolysaccharides and free lipid A from several strains of Rhodospirillaceae were assayed comparatively with those of Enterobacteriaceae in a number of biological tests. Free lipid A's from Rhodopseudomonas gelatinosa and Rhodospirillum tenue exhibited strong serological cross-reactions with each other and with free lipid A from Salmonella. Lipid A's from Rhodopseudomonas viridis and Rhodopseudomonas palustris, although cross-reacting with each other, did not do so with either the lipid A of R. gelatinosa or R. tenue or with that of Salmonella. The presence or absence of the above cross-reactions agreed with corresponding similarities or differences in the chemical structure of the lipid A preparations. The lipopolysaccharide of R. gelatinosa was highly toxic for adrenalectomized mice and pyrogenic for rabbits; however, it exhibited no anti-complementary activity. The activity of the R. tenue lipopolysaccharide was very low in both the lethality and pyrogenicity tests. Its corresponding free lipid A also exhibited low pyrogenic activity; however, its lethal toxicity for adrenalectomized mice was considerably higher than that of the intact parent lipopolysaccharide. Both intact lipopolysaccharide and, unexpectedly, the free lipid A exhibited no anti-complementary activity. The lipopolysaccharides of R. viridis and R. palustris were virtually nontoxic for mice and nonpyrogenic for rabbits. Both lipopolysaccharides were highly potent in their interaction with complement. They therefore represent the first example of nontoxic lipopolysaccharides exhibiting high anti-complementary activity. (+info)
Common lipopolysaccharide specificity: new type of antigen residing in the inner core region of S- and R-form lipopolysaccharides from different families of gram-negative bacteria.
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A new antigenic specificity, referred to here as common lipopolysaccharide (LPS) specificity, is described in the LPSs of gram-negative bacteria belonging to various families. The specificity is present in S- and R-form LPS but absent in Re mutants of different enterobacterial genera. By the use of purified LPS and monospecific antibodies obtained by immunoabsorption, the specificity is differentiated from the known core specificities of the genus Salmonella and the lipid A specificity by aid of the passive hemolysis and passive hemolysis inhibition test. In Salmonella minnesota R-form LPS, the specificity may be cryptic (R345, Rb2 mutant) or partly exposed in the intact molecule (R7, Rd1 mutant). The specificity is either demasked or completely exposed after mild acid hydrolysis for a short time, whereas it is destroyed after prolonged hydrolysis. Periodate oxidation, reduction, and hydrolysis under conditions that do not affect the ketosidic linkages of 2-keto-3-deoxyoctulosonic acid destroy the specificity in R4 (Rd2 mutant) LPS, but do not do so in R7 LPS. It is suggested that 2-keto-3-deoxyoctulosonic acid and a following neutral sugar are the compositional requirements for expressing the specificity. (+info)
Pyridine nucleotide control and subunit structure of phosphoribulokinase from photosynthetic bacteria.
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With one exception, phosphoribulokinase from the Rhodospirillaceae requires reduced nicotinamide adenine dinucleotide for maximum activity. This mode of regulation is unique to the facultatively anaerobic photoorganotrophic photosynthetic bacteria, since the phosphoribulokinase from oxygen-evolving photosynthetic species is not subject to activation by reduced nicotinamide adenine dinucleotide. The enzyme was purified of fructose bisphosphatase activity from Rhodopseudomonas capsulata by means of affinity chromatography and was shown to have a native molecular weight of about 220,000. The homogeneous enzyme is composed of a single size polypeptide of 36,000 molecular weight. This study represents the first time the subunit structure of phosphoribulokinase has been determined from any source. (+info)
Reaction of C-type cytochromes with the iron hexacyanides. Mechanistic implications.
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The reaction of c-cytochromes with iron hexacyanides is similar in mechanism to the interaction of cytochromes with their physiological oxidants and reductants in that the formation of complexes precedes electron transfer. Analysis of the kinetics of oxidation and reduction of a number of c-cytochromes by solving the simultaneous differential equations defining the mechanism is possible, and allows assignment of all six rate constants describing a minimum three-step mechanism [cyto(Fe(+3)) + Fe(+2) right harpoon over left harpoon cyto (Fe(+3)) - Fe(+2) right harpoon over left harpoon cyto(Fe(+2)) - Fe(+3) right harpoon over left harpoon cyto(Fe(+2)) + Fe(+3)]. We find that the usual steady-state approximations are not valid. Furthermore, the ratio of first-order rate constants for electron transfer was approximately 1.0, and no correlation was found between any of the six rate constants and the differences in oxidation-reduction potential of the iron-hexacyanides and different cytochromes c. However, it was found that the ratio of the rate constants for complex formation between ferricytochrome c and potassium ferrocyanide and ferrocytochrome c and potassium ferricyanide was proportional to the difference in oxidation-reduction potentials. Thus the minimum three-step mechanism given above accurately describes the observed kinetic data. However, this mechanism leads to a number of conceptual difficulties. Specifically, the mechanism requires that the collision complexes formed [cyto(Fe(+3)) - Fe(CN)(6) (-4) and cyto(Fe(+2)) - Fe(CN)(6) (-3)] have very different equilibrium constants, and further requires that formation of the collision complexes be accompanied by "chemistry" to make the intermediates isoenergetic. A more complex five-step mechanism which requires that the reactants [Fe(CN)(6) (-4) and ferricytochrome c or Fe(CN)(6) (-3) and ferrocytochrome c] form a collision complex followed by a first-order process before electron transfer, was found to yield results similar to those of the three-step mechanism. However, describing the formation of the collision complex in terms of a rapid equilibrium circumvents conceptual difficulties and leads to a physically reasonable mechanism. In this mechanism the reactants are in rapid equilibrium with the collision complexes and the rate constants for complex formation are controlled by diffusion and accessibility. The collision complexes then rearrange, possibly through conformational changes and/or solvent reorganization, to yield isoenergetic intermediates that can undergo rapid reversible electron transfer. The five-step mechanism can be described by the same rate constants obtained from the three-step mechanism with the appropriate adjustments to account for rapid equilibrium. This more complex analysis associates the oxidation-reduction potential of a particular cytochrome with the relative magnitude of the first-order conversion of the oxidant and reductant collision complexes to their respective intermediates. Thus the cytochromes c control their oxidation-reduction potential by chemical and/or structural alterations. This mechanism appears to be general in that it is consistent with the observed kinetics of 11 different cytochromes c from a wide variety of sources with a range of oxidation-reduction potentials. (+info)
Nitrogen fixation and nitrogenase activities in members of the family Rhodospirillaceae.
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Strains of all 18 species of the family Rhodospirillaceae (nonsulfur photosynthetic bacteria) were studied for their comparative nitrogen-fixing abilities. All species, with the exception of Rhodocyclus purpureus, were capable of growth with N2 as the sole nitrogen source under photosynthetic (anaerobic) conditions. Most rapid growth on N2 was observed in strains of Rhodopseudomonas capsulata. Within the genus Rhodopseudomonas, the species R. capsulata, R. sphaeroides, R. viridis, R. gelatinosa, and R. blastica consistently showed the highest in vivo nitrogenase rates (with the acetylene reduction technique); nitrogenase rates in other species of Rhodopseudomonas and in most species of Rhodospirillum were notably lower. Chemotrophic (dark microaerobic) nitrogen fixation occurred in all species with the exception of one strain of Rhodospirillum fulvum; oxygen requirements for dark N2 fixation varied considerably among species and even within strains of the same species. We conclude that the capacity to fix molecular nitrogen is virtually universal among members of the Rhodospirillaceae but that the efficacy of the process varies considerably among species. (+info)
Structural studies on the phosphate-free lipid A of Rhodomicrobium vannielii ATCC 17100.
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The structure of the free lipid A from Rhodomicrobium vannielii ATCC 17100 was elucidated. It consists of a central beta-1',6-linked glucosamine disaccharide which is not substituted by phosphate. About 30% of the disaccharide molecules are substituted with mannopyranose in beta-1,4'-linkage to the non-reducing glucosamine. The reducing glucosamine can be directly reduced with NaBH4, indicating either that this glucosamine is not substituted at C1 or its substituent has been removed during the preparation of free lipid A or is removed during reduction with NaBH4. The following formula shows the 'backbone' structure of the free lipid A from Rm. vannielii ATCC 17100: beta-Manp(1-- leads to 4)-beta-GlcpN(1 leads to 6)GlcpN. 3-(R)-Hydroxyhexadecanoic acid is linked to the amino group of the reducing glucosamine. The residue at the amino group of the non-reducing glucosamine has not been identified. The hydroxyl groups of the central disaccharide are acylated with 3-(tetradecanoyloxy)-tetradecanoic acid, 3-hydroxytetradecanoic acid, delta 14-docosenoic acid (delta 14-C22:1) and acetyl groups. The hydroxyl groups of the mannose are not substituted. (+info)
Polar lipids in phototrophic bacteria of the Rhodospirillaceae and Chromatiaceae families.
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The polar lipids of photosynthetic purple bacteria of the genera Chromatium, Thiocapsa, Thiocystis, Ectothiorhodospira, Rhodopseudomonas, Rhodospirillum, and Rhodomicrobium were analyzed. Characteristic compositions of the polar lipids were found for most of the Rhodospirillaceae and Chromatiaceae species. Phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin were the major phospholipids in most species. Phosphatidylcholine was present as a major component in all species of the genus Ectothiorhodospira, but was not detected in the remaining Chromatiaceae. It was also present in most of the Rhodospirillaceae species. No glycolipids were found in any of the Ectothiorhodospira species. In the Rhodospirillaceae, the glycolipids mono- and digalactosyl diglycerides were generally absent. Sulfoquinovosyl diglyceride was present in significant amounts in at least three species of the Rhodospirillaceae and may have been present in most of them, but only in traces. All of the Chromatiaceae species contained several glycolipids, one of which was similar to monogalactosyl diglyceride. Ornithine lipids were found in large amounts in most Rhodospirillaceae, but were absent in Ectothiorhodospira and in the other Chromatiaceae. The species examined could be divided into three groups on the basis of their lipid composition: (i) the genus Ectothiorhodospira; (ii) the remaining Chromatiaceae; and (iii) the Rhodospirillaceae. The data presented are compared with those available in the literature, and differences from other phototrophic organisms are discussed. (+info)