Oxidative phosphorylation in Micrococcus dentrificans. II. The properties of pyridine nucleotide transhydrogenase

Physiology of yeasts in relation to biomass yields

The stoichiometric limit to the biomass yield (maximal assimilation of the carbon source) is determined by the amount of CO2 lost in anabolism and the amount of carbon source required for generation of NADPH. This stoichiometric limit may be reached when yeasts utilize formate as an additional energy source. Factors affecting the biomass yield on single substrates are discussed under the following headings: Energy requirement for biomass formation (YATP). YATP depends strongly on the nature of the carbon source. Cell composition. The macroscopic composition of the biomass, and in particular the protein content, has a considerable effect on the ATP requirement for biomass formation. Hence, determination of for instance the protein content of biomass is relevant in studies on bioenergetics. Transport of the carbon source. Active (i.e. energy-requiring) transport, which occurs for a number of sugars and polyols, may contribute significantly to the calculated theoretical ATP requirement for biomass formation. P/O-ratio. The efficiency of mitochondrial energy generation has a strong effect on the cell yield. The P/O-ratio is determined to a major extent by the number of proton-translocating sites in the mitochondrial respiratory chain. Maintenance and environmental factors. Factors such as osmotic stress, heavy metals, oxygen and carbon dioxide pressures, temperature and pH affect the yield of yeasts. Various mechanisms may be involved, often affecting the maintenance energy requirement. Metabolites such as ethanol and weak acids. Ethanol increases the permeability of the plasma membrane, whereas weak acids can act as proton conductors. Energy content of the growth substrate. It has often been attempted in the literature to predict the biomass yield by correlating the energy content of the carbon source (represented by the degree of reduction) to the biomass yield or the percentage assimilation of the carbon source. An analysis of biomass yields of Candida utilis on a large number of carbon sources indicates that the biomass yield is mainly determined by the biochemical pathways leading to biomass formation, rather than by the energy content of the substrate.

The role of iron-sulfur center 2 in electron transport and energy conservation in the NADH-ubiquinone segment of the respiratory chain in Paracoccus denitrificans

1. The electron paramagnetic resonance spectra at 15 K of reduced membrane particles of Paracoccus denitrificans exhibit resonance signals with g values, line shapes and temperature profile which are similar to the signals of the iron-sulfur centers observed in the NADH-ubiquinone segment of mitochondrial respiratory chains. These iron-sulfur centers are reducible with NADH, NADPH as well as chemically with dithionite. 2. Sulphate-limited growth of Paracoccus denitrificans results in the loss of an electron paramagnetic resonance signal (gz approximately 2.05, gy approximately gx approximately 1.92) which has properties similar to those of iron-sulfur center 2 of the NADH dehydrogenase of mitochondrial origin. The loss of this signal is accompanied by a decrease in the NADH oxidase and NADH ferricyanide oxidoreductase activities to respectively 30 and 40% of the values found for succinate-limited growth conditions. In addition respiration in membrane particles from sulphate-limited cells loses its sensitivity to rotenone. 3. Since sulphate-limited growth of Paracoccus denitrificans induces loss of site I phosphorylation [Arch. Microbiol. (1977) 112, 25-34] these observations suggest a close correlation between site I phosphorylation, rotenone-sensitivity and the presence of an electron paramagnetic resonance signal with gz approximately 2.05 and gy approximately gx approximately 1.92.

Transhydrogenase activity in the marine bacterium Beneckea natriegens

The marine bacterium, Beneckea natriegens, which has previously been reported not to form transhydrogenase, has been shown to synthesize a soluble energy-independent transhydrogenase (NADPH:NADP+ oxidoreductase, EC 1.6.1.1), though no energy-linked activity could be detected. The transhydrogenase is induced maximally in stationary phase cells and its formation is 70-90% repressed by raising the medium phosphate level from 0.33 to 3.3 mM. The enzyme is inhibited by arsenate, inorganic ortho- and pyrophosphate and by a range of organic phosphate-containing compounds, including 2'-AMP, which is an activator of several bacterial transhydrogenases.

Conservation and transformation of energy by bacterial membranes

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The energy-linked transhydrogenase reaction in respiratory mutants of Escherichia coli K12

1. Energy-linked and non-energy-linked transhydrogenase activities were assayed in membrane preparations from normal Escherichia coli K 12 and from various mutant strains. 2. The energy-linked transhydrogenase, which uses ATP as energy source, was dependent for activity on the presence of a functional Mg(2+)+Ca(2+)-stimulated adenosine triphosphatase. 3. Neither of the quinones formed by E. coli, namely ubiquinone-8 and menaquinone-8, was required for normal ATP-dependent energy-linked transhydrogenase activity. 4. The energy-linked transhydrogenase was inhibited by piericidin A at a site unrelated to the sites of inhibition of the electron-transport chain by piericidin A.

Studies on energy-linked reactions. Energy-linked transhydrogenase reaction in Escherichia coli

1. Small particles from Escherichia coli catalyse an ATP-dependent reduction of NADP(+) by NADH. 2. The reaction was stimulated by Mg(2+) and only ATP and ITP could serve as energy donors. 3. Studies of the stoicheiometry of the reaction indicate that 1-2mol of ATP are utilized/mol of NADH produced. 4. The reaction is inhibited by uncoupling agents such as 2,4-dinitrophenol (200mum) and tetrachlorotrifluorobenzimidazole (2mum) but oligomycin does not inhibit. 5. The reaction is inhibited by relatively high concentrations (200mum) of piericidin A.

Effects of heat treatment of electron-transport particles on bacterial oxidative phosphorylation

The electron-transport particles from Mycobacterium phlei exhibit low levels of phosphorylation unless supplemented with soluble coupling proteins. Heat treatment of the electron transport particles for 15 min at 50 degrees C was found to result in a slight loss of oxidation and an activation of phosphorylation with NADH as substrate, while with succinate as substrate both activities increased. The heat-activated particles do not require the addition of soluble coupling factors and their level of oxidative phosphorylation is similar to that of the regular particles supplemented with the soluble coupling factors. In contrast to the lack of a requirement for the soluble coupling factors after heat activation, the heat-treated electron-transport particles require the presence of a particulate-bound coupling factor for phosphorylation. The heat-activated system, like the untreated system, was found to be sensitive to uncoupling agents.