Mycobacterium smegmatis fatty acid synthetase. A mechanism based on steady state rates and product distributions

Abstract

The initial steady state rate and product distribution of fatty acid synthesis catalyzed by Mycobacterium smegmatis fatty acid synthetase has been investigated as a function of various concentrations of acetyl-CoA, malonyl-CoA, mycobacterial polysaccharide, and bovine serum albumin. Polysaccharide has a large effect on both rate and chain length. The steady state rate stimulation by polysaccharide is not duplicated by other acyl-CoA-binding molecules such as bovine serum albumin. It is concluded that relief of product inhibition does not adequately explain the specific effects of the mycobacterial polysaccharide. A general mechanism is presented which accounts for variations in reaction rate and produce pattern over a wide range of experimental conditions. We propose that the diffusion of long chain acyl-CoA (C14 to C24) from the enzyme is the rate-limiting step in fatty acid synthesis catalyzed by the M. smegmatis synthetase. Polysaccharide facilitates this rate-limiting step by forming a ternary complex with enzyme-bound acyl-CoA causing rapid release of product.