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

Abstract

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 K _m 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 (α and β) with molecular masses of 53 and 56 kDa, respectively. The enzyme showed maximal activity at pH 7.0–7.5 and at 25–30°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.