FORMATION OF ESTERS FROM ACIDS BY BREWER'S YEAST I. KINETIC THEORY AND BASIC EXPERIMENTS

A study has been made of the formation of some volatile esters in anaerobic fermentation, by Saccharomyces cerevisiae, of a synthetic medium with glucose as the carbon source. The relationship between the rate of formation of ethyl butyrate and the concentration of butyric acid can be expressed by a modification of the Briggs-Haldane equation for monomolecular enzymic reactions; the same is true with ethyl valerate and valeric acid. Butyric acid and valeric acid compete in the ester synthesis, presumably for coenzyme A. The kinetics of such a system of competing substrates is discussed, and the formation of ethyl butyrate and ethyl valerate from butyric acid and valeric acid is shown to satisfy the theory. The constants in the modified Briggs-Haldane equation are calculated for ester formation from butyric acid and valeric acid. The maximum rate is about the same, but the Michaelis constant for butyric acid is about twice that for valeric acid. The formation of ethyl acetate shows some discrepancies. These are discussed.