Comparative studies on the dodecameric and hexameric forms of yeast aminopeptidase I.

Yeast aminopeptidase I, when purified from autolysates of brewer's yeast, is obtained in two molecular froms a) the enzymatically active dodecameric complex (Mr = 640,000, s20,w = 22 S) and b) inactive hexamers (Mr = 320,000, s20,w = 12 S). Although the amino acid composition of the 12 S protein is very similar to that of the active enzyme,the hexamers behave differently in ionic exchange chromatography and during electrophoresis on polyacrylamide gels. Moreover, the antigenic properties of 12 S and 22 S aminopeptidase forms suggest a considerable degree of structural diversity. Several strains of Saccharomyces cerevisiae did not contain hexameric forms although their 22 S aminopeptidase was immunologically indistinguishable from brewer's yeast aminopeptidase. It is proposed that the hexameric protein is the result of "unproductive" aggregation of aminopeptidase subunits.