MALATE METABOLISM BY DESULFOVIBRIO-GIGAS AND ITS LINK TO SULFATE AND FUMARATE REDUCTION - PURIFICATION OF THE MALIC ENZYME AND DETECTION OFNAD(P)(+) TRANSHYDROGENASE ACTIVITY

Malate metabolism was investigated in lactate grown cells of Desulfovi brio gigas; 3 mol of malate are converted into 2 mol succinate and 1 m ol acetate. The malic enzyme (L-malate:NADP(+) oxidoreductase) was pur ified to homogeneity and partially characterized. The enzyme is monome ric with molecular weight of 45 kDa. Its spectrum has no visible absor ption and the activity is stimulated by K+ and Mg2+. The presence of a n NAD(P)(+) transhydrogenase, the observation of partial reduction of adenylylsulfate reductase by NADH (via NADH-rubredoxin oxidoreductase) and evidence for NADH-linked fumarate reductase activity support the involvement of pyridine nucleotides in the electron pathway toward the reduction of sulfur compounds and/or fumarate. An electron transfer c hain to fumarate is proposed, taking into consideration these results and the stoichiometry of end-products derived from malate dismutation. (C) 1995 Academic Press