Further analysis of acyl-CoA-ACP-transacylases of mycobacterium smegmatis. Identification of a long chain alkyl malonyl-CoA-ACP-transacylase.

Homogenates were prepared from three sources, Mycobacterium smegmatis Saccharomyces cerevisiae and Escherichia coli and tested for docosyl malonyl-CoA-ACP transacylase activity, using ACP purified from E. coli strain B and [2R, 2S, 1, 3-14C2] docosyl malonyl-CoA synthesized chemically, as substrates. Only homogenates of M. semegmatis showed positive transacylase activity. Successive chromatographies on Sephadex G-150 and then on DEAE-Sephadex A-50 prove that neither the palmityl-CoA-ACP-transacylase nor the malonyl-CoA-ACP-transacylase of M. smegmatis are responsible for this activity. The question concerning the identity of the enzyme with one of the two entities exhibiting acetyl-CoA-ACP-transacylase activity, previously identified in homogenates of this microorganism (1973 this journal, 55, 1381-1394), remains open for further experimentation. The physiological significance of the presence of a long chain alkyl malonyl-CoA-ACP-transacylase in homogenates of M. smegmatis, a representative of the Actinomycetales, is discussed in relation to the mechanism of the biosynthesis of mycolic acids. Chromatography on Sephadex G-100 showed that the substrate of the enzyme, docosyl malonyl-CoA, exists, in 50 mu molar aqueous solution, mostly in an aggregated state. A factor has been identified in the homogenates, which in the presence of radioactive docosyl malonyl-CoA, leads to the formation of a radioactive material showing an apparent molecular weight less than 10000. The nature of this material is discussed.