Martin Bokranz

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

Abstract1.Growth of Vibrio succinogenes with nitrate as terminal electron acceptor was found to be a function of the following two catabolic reactions: (a)

ATP formation coupled to caffeate reduction by H2 in Acetobacterium woodii NZva16

HCO _2^ - + NO _3^ - + H^ + \to CO_2 + NO _2^ - + H_2 O

Electron transport driven phosphorylation catalyzed by proteoliposomes containing hydrogenase, fumarate reductase and ATP synthase

(b)

The membraneous nitrite reductase involved in the electron transport of Wolinella succinogenes

3HCO _2^ - + NO _2^ - + 5H^ + \to 3CO_2 + NH _4^ + + 2H_2 O.

Structural and ATP-hydrolyzing properties of the ATP synthase isolated from Wolinella succinogenes

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.

Methyl-coenzyme-M reductase from Methanobacterium thermoautotrophicum (strain Marburg). Purity, activity and novel inhibitors.

SummaryThe sequence of the gene cluster encoding the methyl coenzyme M reductase (MCR) in Methanococcus voltae was determined. It contains five open reading frames (ORF), three of which encode the known enzyme subunits. Putative ribosome binding sites were found in front of all ORFs. They differ in their degrees of complementarity to the 3′ end of the 16 S rRNA, which is discussed in terms of different translation efficiencies of the respective genes. The codon usage bias is different in the subunit encoding genes compared with the two other ORFs in the cluster and two other known genes of Mc. voltae. This is interpreted in terms of increased translational accuracy of the highly expressed MCR subunit genes. The derived polypeptide sequences encoded by the five ORFs of the MCR cluster were compared to those of the respective genes in Methanobacterium thermoautotrophicum Marburg and Methanosarcina barkeri. Conserved regions were detected in the enzyme subunits, which are candidates for factor binding domains. Conserved hydrophobic sequences found in the α and β subunits are discussed with respect to the membrane association of the enzyme.