The molybdenum cofactor biosynthesis protein MobA from Rhodobacter capsulatus is required for the activity of molybdenum enzymes containing MGD, but not for xanthine dehydrogenase harboring the MPT cofactor

The requirement of MobA for molybdoenzymes with different molybdenum cofact ors was analyzed in Rhodobacter capsulatus. MobA is essential for DMSO redu ctase and nitrate reductase activity, both enzymes containing the molybdopt erin guanine dinucleotide cofactor (MGD), but not for active xanthine dehyd rogenase,, harboring the molybdopterin cofactor. In contrast to the nob loc us of Escherichia coli and R. sphaeroides; the mobB gene is not located dow nstream of mobA in R. capsulatus. The mobA gene is expressed constitutively at low levels and no increase in mobA expression could be observed even un der conditions of high MGD demand. (C) 1999 Federation of European Microbio logical Societies.-Published by Elsevier Science B.V. All rights reserved.