Malonate decarboxylase of Pseudomonas putida is composed of five subunits.

Two different forms of malonate decarboxylase were purified from Pseudomonas putida. The active form was composed of the five different subunits alpha (60 kDa), beta (33 kDa), gamma (28 kDa), delta (13 kDa), and epsilon (30 kDa) and the inactive form was composed of the four subunits lacking the epsilon subunit. The former catalyzed the decarboxylation of malonate to acetate, but the latter could not, although it retained both activities of acetyl-CoA:malonate CoA transferase and malonyl-CoA decarboxylase. The delta subunit of the active form was acylated by the incubation with [2-14C]malonyl-CoA, but the delta subunit of the inactive form was not labeled. From the above results and the N-terminal amino acid sequence analysis, it was concluded that the epsilon subunit was an essential subunit to function as malonyl-CoA:ACP transacylase, which was an indispensable component of the enzyme for the cyclic decarboxylation of malonate.