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H Gest

Publications and source records attributed to H Gest.

At least 55 records · Page 3Linked to original sources
PubMed1977

H2 metabolism in the photosynthetic bacterium Rhodopseudomonas capsulata: H2 production by growing cultures.

Purple photosynthetic bacteria produce H2 from organic compounds by an anaerobic light-dependent electron transfer process in which nitrogenase functions as the terminal catalyst. It has been established that the H2-evolving function of nitrogenase is inhibited by N2 and ammonium salts, and is maximally expressed in cells growing photoheterotrophically with certain amino acids as sources of nitrogen. In the present studies with Rhodopseudomonas capsulata, nutritional factors affecting the rate and magnitude of H2 photoproduction in cultures growing with amino acid nitrogen sources were examined. The highest H2 yields and rates of formation were observed with the organic acids: lactate, pyruvate, malate, and succinate in media containing glutamate as the N source; under optimal conditions with excess lactate, H2 was produced at rates of ca. 130 ml/h per g(dry weight) of cells. Hydrogen production is significantly influenced by the N/C ratio in the growth substrates; when this ratio exceeds a critical value, free ammonia appears in the medium and H2 is not evolved. In the "standard" lactate + glutamate system, both H2 production and growth are "saturated" at a light intesity of ca. 600 ft-c (6,500 lux). Evolution of H2, however, occurs during growth at lithe intensities as low as 50 to 100 ft-c (540 to 1,080 lux), i.e., under conditions of energy limitation. In circumstances in which energy conversion rate and supplies of reducing power exceed the capacity of the biosynthetic machinery, energy-dependent H2 production presumably represents a regulatory device that facilitates "energy-idling." It appears that even when light intensity (energy) is limiting, a significant fraction of the available reducing power and adenosine 5'-triphosphate is diverted to nitrogenase, resulting in H2 formation and a bioenergetic burden to the cell.

Amino Acids↗
PubMed1977

H2 metabolism in the photosynthetic bacterium Rhodopseudomonas capsulata: production and utilization of H2 by resting cells.

Photoproduction of H2 and activation of H2 for CO2 reduction (photoreduction) by Rhodopseudomonas capsulata are catalyzed by different enzyme systems. Formation of H2 from organic compounds is mediated by nitrogenase and is nto inhibited by an atmosphere of 99% H2. Cells grown photoheterotrophically on C4 dicarboxylic acids (with glutamate as N source) evolve H2 from the C4 acids and also from lactate and pyruvate; cells grown on C3 carbon sources, however, are inactive with the C4 acids, presumably because they lack inducible transport systems. Ammonia is known to inhibit N2 fixation by photosynthetic bacteria, and it also effectively prevents photoproduction of H2; these effects are due to inhibition and, in part, inactivation of nitrogenase. Biosynthesis of the latter, as measured by both H2 production and acetylene reduction assays, is markedly increased when cells are grown at high light intensity; synthesis of the photoreduction system, on the other hand, is not appreciably influenced by light intensity during photoheterotrophic growth. The photoreduction activity of cells grown on lactate + glutamate (which contain active nitrogenase) is greatly activated by NH4+, but this effect is not observed in cells grown with NH4+ as N source (nitrogenase repressed) or in a Nif- mutant that is unable to produce H2. Lactate, malate, and succinate, which are readily used as growth substrates by R. capsulata and are excellent H donors for photoproduction of H2, abolish photoreduction activity. The physiological significances of this phenomenon and of the reciprocal regulatory effects of NH4+ on H2 production and photoreduction are discussed.

Ammonia↗
PubMed1976

Inorganic nitrogen assimilation by the photosynthetic bacterium Rhodopseudomonas capsulata.

The photosynthetic bacterium Rhodopseudomonas capsulata lacks glutamate dehydrogenase and normally uses the glutamine synthetase/glutamate synthase sequence of reactions for assimilation of N2 and ammonia. The glutamine synthetase in cell-free extracts of the organism is completely sedimented by centrifugation at 140,000 X g for 2 h, is inhibited by L-alanine but not by adenosine 5'-monophosphate, and exhibits two apparent Km values for ammonia (ca. 13 muM and 1 mM).

Adenosine Monophosphate↗
PubMed1975

Characterization of Rhodopseudomonas capsulata.

Thirty-three strains of Rhodopseudomonas capsulata have been studied in order to develop a more comprehensive characterization of the species. On the basis of morphological, nutritional, physiological and other properties, the characteristics of an "ideal biotype" have been defined, which can be used to distinguish Rps. capsulata from similar purple bacteria. In this connection, two properties of Rps. capsulata are of particular note: a) sensitivity to penicillin G is 10(3)-10(5) times greater than that shown by closely related species, and b) all strains examined are susceptible to lysis by one or more strains of host species-specific virulent bacteriophages. It appears that members of the species Rps. capsulata form a stringent taxonomic grouping.

Anaerobiosis↗
PubMed1975

Gene transfer agents, bacteriophages, and bacteriocins of Rhodopseudomonas capsulata.

Thirty-three wild type strains of Rhodopseudomonas capsulata were examined for ability to engage in genetic recombination through mediation by "gene transfer agent" (GTA) particles. The genetic exchange assays were based on capacity of strains to produce or receive GTA required for restoration of photosynthetic growth competence to a non-photosynthetic "white" mutant or for acquisition of resistance to rifampicin. A majority of the strains could either produce or receive GTA, and it was demonstrated that the agent is species specific. Possible relations between GTA and bacteriophages or bacteriocins were investigated. Sixteen types of virulent phages active on Rps. capsulata were isolated and their host ranges determined. Tests for transduction by the phages gave uniformly negative results. The viruses showed strict species specificity, but there was no apparent correlation between capacity of the Rps. capsulata strains to donate or receive GTA and susceptibility to the phages. A comparable survey disclosed that most of the bacterial strains were sensitive to or capable of producing bacteriocins; the latter also appear to be unrelated to GTA activity. The collection of bacterial strains was also screened for detection of lysogenic properties. None of the isolates is a "true" lysogen, but phages were detected in cultures of two strains, which may be "phage carriers" or pseudolysogens.

Bacteriocins↗
PubMed1973

Genetic mutations affecting the respiratory electron-transport system of the photosynthetic bacterium Rhodopseudomonas capsulata.

Alternative energy-converting systems permit the nonsulfur purple photosynthetic bacterium Rhodopseudomonas capsulata to grow either with light or (dark) respiration as the source of energy. Respiratory mutants, unable to grow aerobically in darkness, can be readily isolated and the defective step(s) in their respiratory mechanisms can be identified by study of biochemical activities in membrane fragments derived from photosynthetically grown cells. Such analysis of appropriate mutants and revertants permits construction of a model for the respiratory electron-transport system of the wild type. The results obtained indicate differential channeling of electrons derived from succinate and reduced nicotinamide adenine dinucleotide, and are interpreted in terms of a branched electron-transport scheme. The scheme provides a guide for further, more refined analysis of the respiratory mechanisms through biochemical genetic approaches, and several of the mutants isolated can be exploited for investigation of unsolved problems relating to interactions between respiratory and photosynthetic electron transport and the mechanism of inhibition of bacteriochlorophyll synthesis by molecular oxygen.

Antimycin A↗
PubMed1973

Regulation of bacteriochlorophyll synthesis by oxygen in respiratory mutants of Rhodopseudomonas capsulata.

Respiratory mutants of the facultative photosynthetic bacterium Rhodopseudomonas capsulata were used to investigate the mechanism of (reversible) inhibition of bacteriochlorophyll (BChl) synthesis by molecular oxygen. Although mutant strain M5 lacks cytochrome oxidase activity, it closely resembles the parental wild-type strain in respect to the effect of O(2) on BChl formation. This observation does not support an earlier hypothesis that O(2) regulates BChl synthesis through an effect on the redox state of a component of the respiratory electron transport system. Mutant strain M2 shows normal cytochrome oxidase activity, but lacks both reduced nicotinamide adenine dinucleotide and succinate dehydrogenase activities; relative to the parental strain, BChl synthesis in M2 is more sensitive to O(2) inhibition. The foregoing and results of related experiments can be accounted for by a revised interpretation of the O(2) effect, which proposes that O(2) directly inactivates a "factor" necessary for BChl formation and that, at relatively low O(2) tension, the inactivation can be reversed by a flow of electrons (derived from reduced nicotinamide adenine dinucleotide and succinate) diverted from a portion of the electron transport system delimited by the mutational blocks in M2 and M5.

Chlorophyll↗
PubMed1972

Biochemical physiology of a respiration-deficient mutant of the photosynthetic bacterium Rhodopseudomonas capsulata.

Nonsulfur purple photosynthetic bacteria generally possess the adaptive capacity to grow anaerobically (photosynthetically) and aerobically in darkness (energy obtained by respiratory phosphorylation). To develop a test system for study of interactions between the photosynthetic energy-conversion and dark respiration systems and the mechanism by which O(2) inhibits bacteriochlorophyll synthesis, we have isolated a mutant of Rhodopseudomonas capsulata that is incapable of dark aerobic growth. Both the parent strain and the mutant strain Z-1 (aer-13) grow readily anaerobically in the light with either malate or succinate as the source of carbon and reducing power. They differ, however, in that membrane fragments ("chromatophores") from the mutant show severely impaired ability to use reduced nicotinamideadenine dinucleotide (NADH) as a source of electrons for respiration, oxidative phosphorylation, or "redox buffering" of the photophosphorylation system. The results presented indicate that the genetic lesion responsible for greatly diminished capacity to oxidize NADH can account for inability of Rps. capsulata Z-1 (aer-13) to grow aerobically in darkness.

Aerobiosis↗
PubMed1971

Interchangeability of phosphorylation coupling factors in photosynthetic and respiratory energy conversion.

The nonsulfur purple photosynthetic bacterium Rhodopseudomonas capsulata can obtain energy for growth either by anaerobic photophosphorylation or dark oxidative (aerobic) phosphorylation. Successful resolution of phosphorylation coupling factors from energy-converting membranes of this bacterium permitted tests for reciprocal function of such protein factors in oxidative-and photophosphorylation processes. Evidence was obtained for the interchangeability of coupling factor preparations from dark-grown and photosynthetically grown cells in both kinds of energy conversion.

Aerobiosis↗
PubMed1971

Regulatory properties of an inorganic pyrophosphatase from the photosynthic bacterium Rhodospirillum rubrum.

In Rhodospirillum rubrum, inorganic pyrophosphatase activity is observed in both the cytoplasmic and membrane fractions. The soluble enzyme accounts for about 80% of the total activity in crude extracts, and is the subject of this report. Zn(2+) is required for both activity and stability of the enzyme, which has a molecular weight of approximately 90,000 (gel-filtration determinations). The substrate is MgP(2)O(7) (2-), and free pyrophosphate (P(2)O(7) (4-)) is a strong inhibitor. Kinetic experiments indicate homotropic interactions between substrate-binding sites; these interactions are influenced by Mg(2+), which is an activator. At low concentrations of Zn(2+), the pyrophosphatase is inhibited by NADH, NADPH, and MgATP; 50% inhibition occurs at 0.4-0.7 mM. These effects are reversed by high concentrations of Zn(2+) (10(-4)-10(-3) M). The nucleotides appear to inhibit activity of the "native" enzyme through an effect on Zn(2+) binding. The R. rubrum enzyme seems to be the first known example of a bacterial inorganic pyrophosphatase subject to allosteric regulation.

Adenosine Triphosphate↗
PubMed1971

Mutational and physiological enhancement of photosynthetic energy conversion in Rhodopseudomonas capsulata.

Photosynthetic growth of Rhodopseudomonas capsulata, a nonsulfur purple bacterium, is severely inhibited by inorganic arsenate when this anion is present equimolar to orthophosphate in the culture medium. Studies on an arsenate-resistant mutant indicate that its resistance can be explained by a significantly increased photophosphorylation capacity of the energy-converting machinery, which can compensate for the decrease in adenosine triphosphate regeneration rate caused by esterification of arsenate in place of phosphate. Repeated subculture of the mutant in the presence of arsenate, under certain conditions, yields cell populations that have strikingly elevated contents of membrane-bound reaction-center bacteriochlorophyll, cytochromes, and photo-phosphorylation coupling factor. Membranes from such cells show unusually high photophosphorylation activity, and can be expected to provide a useful experimental material for more refined analysis of the mechanism of the energy-conversion process.

Adenosine Triphosphate↗