Specific modification of fatty acid synthetase from lactating rat mammary gland by chymotrypsin and trypsin.

Fatty acid synthetase from lactating rat mammary gland after limited proteolysis with chymotrypsin or trypsin synthesizes longer chain fatty acids than those produced by the native enzyme. Of the seven partial reactions of the multienzyme complex, only the thioesterase activity was decreased. The results suggest that modification of the fatty acid synthetase product specificity by chymotrypsin and trypsin results from a specific action of these proteases on the thioesterase component. Trypsin, but not chymotrypsin, cleaved a catalytically active thioesterase from the complex; it thus appears that limited trypsinization will be a useful tool for the isolation of the thioesterase component of the multienzyme.