Cytochrome c-dependent methacrylate reductase from Geobacter sulfurreducens AM-1

Geobacter sulfurreducens AM-1 can use methacrylate as a terminal electron acceptor for anaerobic respiration. In this paper, we report on the purification and properties of the periplasmic methacrylate reductase, and show that the enzyme is dependent on the presence of a periplasmic cytochrome c (apparent K(m) = 0.12 microM). The methacrylate reductase was found to be composed of only one polypeptide with an apparent molecular mass of 50 kDa and to contain, bound tightly but not covalently, 1 mol of FAD per mol. The N-terminal amino acid sequence showed sequence similarity to a periplasmic fumarate reductase from Shewanella putrefaciens. However, methacrylate reductase did not catalyze the reduction of fumarate. The periplasmic cytochrome c, which was also purified, had an apparent molecular mass of 30 kDa and contained approximately 4 mol of heme.mol(-1). Cells of G. sulfurreducens AM-1 grown on acetate and methacrylate as an energy source were found to contain all the enzymes required for the oxidation of acetate to CO(2) via the citric acid cycle.