The architecture of the animal fatty acid synthetase. I. Proteolytic dissection and peptide mapping.

The vertebrate fatty acid synthetase complex consists of two, apparently identical, subunits which contain seven catalytic centers and an acyl carrier site. As a prelude to studying the functional organization of this system, a comprehensive proteolytic analysis of the chicken fatty acid synthetase subunit has been carried out. Of 24 proteases tested, seven (chymotrypsin, elastase, trypsin, Myxobacter protease, subtilisins A and B, and kallikrein) were found to be capable of inflicting specific cleavages in the native enzyme. The proteolytic profiles were analyzed with respect to both the kinetics and the size of the fragments generated. The relationships between the various fragments were further delineated by combinatorial digestions. All of the data points to the fact that the subunits are indeed identical. The cleavage patterns indicate that the fatty acid synthetase subunit is primarily arranged into three major domains of Mr 127,000, 107,000, and 33,000, since these fragments are commonly produced by most of the proteases. The latter peptides may be further subdivided and mapped by the action of individual enzymes into a number of distinct regions: the 127,000 domain into fragments of Mr 60,000, 45,000, and 23,000; the 107,000 domain into fragments of Mr 14,000, 56,000, 21,000, and 15,000; all aligned accordingly. This proteolytic map serves as a reference for the controlled dissection of the fatty acid synthetase complex, thereby allowing determination of the location of functional centers within the parent polypeptide.