The structure and mechanism of iron-hydrogenases

Article synthese concernant les effets des ionophores, en particulier la monensine, sur l'ecologie, sur le metabolisme microbien, et la physiologie membranaire de la flore microbienne des ruminants

Effect of ionophores on ruminal fermentation.

Dissimilatory Sulfate- and Sulfur-Reducing Prokaryotes

The ADP and ATP transport in mitochondria and its carrier

The effect of different electron acceptors on substrate degradation was studied in pure and mixed cultures of various hydrogenotrophic homoacetogenic, methanogenic, sulfate-reducing, fumarate-reducing and nitrate-ammonifying bacteria. Two different species of these bacteria which during organic substrate degradation produce and consume hydrogen, were cocultured on a substrate which was utilized only by one of them. Hydrogen, which was excreted as intermediate by the first strain (and reoxidized in pure culture), could, depending on the hydrogen acceptor present, also be used by the second organism, resulting in interspecies hydrogen transfer. The efficiency of H2 transfer was similar when methanol, lactate or fructose were used as organic substrate, although the free energy changes of fermentative H2 formation of these substrates are considerably different. In coculture experiments nitrate or fumarate>sulfate> CO2/CH4>sulfur or CO2/acetate were the preferred electron acceptors, and an increasing percentage of H2 was transferred to that bacterium which was able to utilize the preferred electron acceptor. In pure culture the threshold values for hydrogen oxidation decreased in the same order from ≤1,100 ppm for homoacetogenic bacteria to about 0.03 ppm for nitrate or fumarate reducing bacteria. The determined H2-threshold values as well as the percentage of H2 transfer in cocultures were related to the Gibbs free energy change of the respective hydrogen oxidizing reaction.

/pdf/the-capacity-of-hydrogenotrophic-anaerobic-bacteria-to-13x9osleu2.pdf

The capacity of hydrogenotrophic anaerobic bacteria to compete for traces of hydrogen depends on the redox potential of the terminal electron acceptor

1.

Growth of Vibrio succinogenes with nitrate as terminal electron acceptor was found to be a function of the following two catabolic reactions: 

$$HCO _2^ - + NO _3^ - + H^ + \to CO_2 + NO _2^ - + H_2 O$$

(a)



$$3HCO _2^ - + NO _2^ - + 5H^ + \to 3CO_2 + NH _4^ + + 2H_2 O.$$

(b)



The latter reaction (b) was responsible for growth with nitrite.




2.

Either succinate or fumarate could serve as sole carbon source during growth with nitrate or nitrite. Biosynthesis from succinate proceeded via fumarate. The ATP requirement for cell synthesis from succinate was equal to that calculated earlier for growth with fumarate as carbon source and electron acceptor (Brounder et al. 1982).




3.

The cell yield at infinite dilution rate (Ymax) as obtained with chemostat cultures was 8.5g dry cells/mol formate with either nitrate or nitrite as acceptor. This value amounts to 60% of that measured earlier with fumarate as acceptor (Mell et al. 1982).




4.

Membrane vesicles prepared from V. succinogenes catalyzed electron transport from H2 to nitrate. The reaction was dependent on the menaquinone present in the membrane.




5.

Electron transport with H2 and nitrite was coupled to the phosphorylation of ADP. The P/H2 ratio with nitrite was 40% of that measured with fumarate as acceptor using the same preparation. The phosphorylation but not the electron transport was abolished by an uncoupling agent.

Energy metabolism and biosynthesis of Vibrio succinogenes growing with nitrate or nitrite as terminal electron acceptor

1.

With fumarate as the terminal electron acceptor and either H2 or formate as donor, Vibrio succinogenes could grow anaerobically in a mineral medium using fumarate as the sole carbon source. Both the growth rate and the cell yield were increased when glutamate was also present in the medium.




2.

Glutamate was incorporated only into the amino acids of the glutamate family (glutamate, glutamine, proline and arginine) of the protein. The residual cell constituents were synthesized from fumarate.




3.

Pyruvate and phosphoenolpyruvate, as the central intermediates of most of the cell constituents, were formed through the action of malic enzyme and phosphoenolpyruvate synthetase. Fructose-1,6-bisphosphate aldolase was present in the bacterium suggesting that this enzyme is involved in carbohydrate synthesis.




4.

In the absence of added glutamate the amino acids of the glutamate family were synthesized from fumarate via citrate. The enzymes involved in glutamate synthesis were present.




5.

During growth in the presence of glutamate, net reducing equivalents were needed for cell synthesis. Glutamate and not H2 or formate was used as the source of these reducing equivalents. For this purpose part of the glutamate was oxidized to yield succinate and CO2.




6.

The α-ketoglutarate dehydrogenase involved in this reaction was found to use ferredoxin as the electron acceptor. The ferredoxin of the bacterium was reoxidized by means of a NADP-ferredoxin oxidoreductase. Enzymes catalyzing the reduction of NAD, NADP or ferredoxin by H2 or formate were not detected in the bacterium.

Biosynthetic pathways of Vibrio succinogenes growing with fumarate as terminal electron acceptor and sole carbon source

Properties and functions of the respiratory chain and of the nucleotide system were studied in mitochondria from Saccharomyces carlsbergensis and compared with those in mitochondria from mammalian tissues.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1967.tb00074.x

The response of the respiratory chain and adenine nucleotide system to oxidative phosphorylation in yeast mitochondria.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2882%2980173-7

A. Kröger

Papers

Energy metabolism and biosynthesis of Vibrio succinogenes growing with nitrate or nitrite as terminal electron acceptor

Biosynthetic pathways of Vibrio succinogenes growing with fumarate as terminal electron acceptor and sole carbon source

The response of the respiratory chain and adenine nucleotide system to oxidative phosphorylation in yeast mitochondria.

Hydrogenase from Vibrio succinogenes, a nickel protein.

Direct evidence for sulphur as a ligand to nickel in hydrogenase: an EPR study of the enzyme from Wolinella succinogenes enriched in 33S