Studies on Yeast Enolase

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.