Fatty acid synthetase activity in Mycobacterium smegmatis. Characterization of the acyl carrier protein-dependent elongating system

Mycobacterium smegmatis extracts contain two fatty acyl synthetase systems (Brindley, D.N., Matsumura, S. and Bloch, K. (1966) Nature 224, 666-669). One is the extensively studied multienzyme complex, (molecular weight 1.39 - 10(6)) which produces shorter C16 and C18) and longer (C24 and higher) fatty acids in a bimodal pattern. The second synthetase is acyl carrier-protein (ACP) dependent and elongates the CoA derivatives of C12 and longer chains. In contrast to the type I synthetase which also extends long fatty acyl chains, the ACP-dependent system produces homologous fatty acids up to 30 carbon atoms long in approximately equal proportions. Other properties which distinguish the ACP-dependent system from the multienzyme complex include the resistance to high concentrations of palmitoyl-CoA and to low ionic strength and the lack of stimulation by mycobacterial polysaccharides. The possibility that the two fatty acid synthetases are complimentary in their function is discussed.