PURIFICATION AND CHARACTERIZATION OF A MONOMERIC ISOCITRATE DEHYDROGENASE FROM THE SULFATE-REDUCING BACTERIUM DESULFOBACTER-VIBRIOFORMIS AND DEMONSTRATION OF THE PRESENCE OF A MONOMERIC ENZYME IN OTHER BACTERIA

NADP(+)-specific isocitrate dehydrogenase (EC 1.1.1.42) was purified t o homogeneity from the sulfate-reducing bacterium Desulfobacter vibrio formis, and shown to be a monomeric protein with a molecular mass of 8 0 kDa. The pH and temperature optima were 8.5 and 45 degrees C respect ively. The N-terminal amino acid sequence (Thr, Glu, Thr, Ile, Arg, Tr p, Thr, X, Thr, Asp, Glu, Ala, Pro, Leu, Leu, Ala, Thr) showed similar ity with that of other known monomeric isocitrate dehydrogenases. Cata lytically active isocitrate dehydrogenase from D. vibrioformis was obt ained by activity staining after SDS-PAGE and removal of SDS from the gel. This technique revealed a NADP(+)-dependent monomeric enzyme in o ther Desulfobacter spp., Desulfuromonas acetoxidans and Chlorobium tep idium. These findings imply that monomeric isocitrate dehydrogenases a re present in distantly related bacteria and indicate an early evoluti on of monomeric isocitrate dehydrogenases in the bacterial lineage. (C ) 1998 Federation of European Microbiological Societies, Published by Elsevier Science B.V.