Studies on Yeast Enolase: QUANTITATIVE END GROUP ANALYSES AND THE EFFECT OF EXOPEPTIDASE DIGESTION

Abstract

Abstract The structural model of yeast enolase has undergone substantial modification in recent years, and the quantitative end group analysis of the enzyme was undertaken as a means of establishing the most recent two-subunit model by a chemical method. Carboxypeptidase digestion and hydrazinolysis gave 1.95 and 1.85 moles, respectively, of carboxyl-terminal leucine per mole of enzyme, and amino-terminal analysis by the cyanate method gave 1.8 moles of amino-terminal alanine per mole of enzyme, thus confirming the model of yeast enolase as an 88,000-dalton protein consisting of two 44,000-dalton subunits. Contrary to reports in the literature, pure enolase was found to be very resistant to endopeptidase-free exopeptidase digestion. The earlier findings that large segments of both the amino-terminal and carboxyl-terminal sequences can be removed by exopeptidases without loss of enolase activity can thus not be reproduced in this laboratory. Some possible reasons for this discrepancy are discussed.