Abstract
Abstract The fatty acid synthetase from Mycobacterium phlei has been purified 340-fold to homogeneity. The enzyme has a molecular weight of 1.39 x 106. At low concentrations of phosphate buffer (0.005 m), the synthetase dissociates into an enzymatically inactive species (7.65 S) which can be partially reaggregated and reactivated by dialysis against 0.5 m potassium phosphate buffer. The mycobacterial polysaccharides, 3-O-methylmannose-containing polysaccharide (MMP) and 6-O-methylglucose-containing polysaccharide (MGLP), stimulate the fatty acid synthetase markedly. Their presence lowers the Km values for acetyl-CoA and malonyl-CoA 9-fold and 4-fold, respectively. The polysaccharides also appear to function by altering the rate-limiting step of fatty acid synthesis. MMP stimulates fatty acid synthesis more effectively than MGLP. Various chemical modifications of the polysaccharides do not markedly alter their stimulating activity. Acetyl-CoA is the most effective primer and its concentration affects the degree to which MMP and MGLP stimulate fatty acid synthesis. It is proposed that the polysaccharides function primarily by binding long chain acyl-CoA and thereby relieve product inhibition of the fatty acid synthetase.
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