Propionyl-CoA carboxylase of Myxococcus xanthus: catalytic properties and function in developing cells.

An acyl-coenzyme A carboxylase that carboxylates acetyl-CoA, butyryl-CoA, propionyl-CoA, and succinyl-CoA was purified from Myxococcus xanthus. Since the enzyme showed maximal rates of carboxylation with propionyl-CoA, the enzyme is thought to be propionyl-CoA carboxylase. The apparent Km values for acetyl-CoA, butyryl-CoA, propionyl-CoA, and succinyl-CoA were found to be 0.2, 0. 2, 0.03, and 1.0 mM, respectively. The native enzyme has a molecular mass of 605-615 kDa and is composed of nonidentical subunits (alpha and beta) with molecular masses of 53 and 56 kDa, respectively. The enzyme showed maximal activity at pH 7.0-7.5 and at 25-30 degrees C, and was affected by variation in concentrations of ATP and Mg2+. During development of M. xanthus, the propionyl-CoA carboxylase activity increased gradually, with maximum activity observed during the sporulation stage. Previous work has shown that a propionyl-CoA-carboxylase-deficient mutant of M. xanthus reduces levels of long-chain fatty acids. These results suggest that the propionyl-CoA carboxylase is also responsible for the carboxylation of acetyl-CoA to malonyl-CoA used for the synthesis of long-chain fatty acids during development.