CARBON ASSIMILATION BY PSEUDOMONAS OXALATICUS (OX 1). 7. DECARBOXYLATION OF OXALYL-COENZYME A TO FORMYL-COENZYME A

Abstract

Cell-free extracts of oxalate-grown P. oxalaticus catalyze the decarboxylation of oxalyl-CoA and the decarboxylation of oxalate in the presence of catalytic quantities of oxalyl-CoA. An enzyme from the cell-free extract catalyzes the decarboxylation of oxalyl-CoA to formyl-CoA. The formyl-CoA was characterized by chromatography, electrophoresis, formation of hydroxamate, absorption spectrum and hydrolysis to formate. Formyl-CoA initiates the decarboxylation of oxalate by crude extracts of P. oxalaticus. The oxalyl-CoA decarboxylase requires thiamine pyrophosphate as cofactor and is stimulated by Mg2+ or Mn2+ ions. The decarboxylation is unaffected by the presence of iodoacetate or N-ethylmaleimide. The pH optimum for the decarboxylation is 6.6. There is no evidence for reversibility of the reaction. Km for oxalyl-CoA is 1 mM. The enzyme did not catalyze the decarboxylation of oxalate, malonate, succinate, malonyl-CoA or succinyl-CoA. Oxalyl-CoA decarboxylase occurs in P. oxalaticus only when grown on oxalate. Possible reaction mechanisms for the decarboxylation of oxalyl-CoA are discussed.