Purification and characterization of S-acyl fatty acid synthase thioester hydrolase which modifies the product specificity of fatty acid synthase in the uropygial gland of mallard.

A thioesterase present in the uropygial gland of mallard functions in conjunction with fatty acid synthase to produce short chain acids in this gland (deRenobales, M., Rogers, L., and Kolattukudy, P. E. (1980) Arch. Biochem. Biophys. 205,464-477). This enzyme, capable of releasing short chain acids from fatty acid synthase, was purified to near homogeneity. This S-acyl fatty acid synthase thioester hydrolase is a monomer with Mr = 29,500 and its amino acid composition is significantly different from those of other thioesterases. It catalyzes hydrolysis of CoA esters maximally at pH 6.5-8.0 and it regenerates the overall activity of phenylmethanesulfonyl fluoride-treated synthase. With CoA ester substrates, this enzyme showed preference for Clz and Cl0 whereas Ce, Cs, C14, C16, and C18 showed 30-50% of the rate obtained with Clz. This specificity was significantly different from that of two other thioesterases from the same gland. The acyl fatty acid synthase hydrolase was inhibited by reagents directed against active serine and histidine, strongly suggesting that it is a serine esterase. This enzyme was also highly sensitive to thiol-directed reagents. The acyl fatty acid synthase hydrolase activity, but not the CoA esterase activity, was inhibited by high ionic strength. This hydrolase was nearly as effective in regenerating the overall activity of phenylmethanesulfonyl fluoridetreated fatty acid synthase from rat mammary gland as a similar hydrolase obtained from the mammary gland. On the other hand, with the avian fatty acid synthase, the avian hydrolase was 20-30 times more efficient than the hydrolase from the rat mammary gland. The occurrence of ample amounts of acyl fatty acid synthase hydrolase specifically in the glands which produce short chain acids strongly suggests that this hydrolase is involved in the production of the short chain acids in these specialized glands.