A New Model for the Regulation of Ester Synthesis by Alcohol Acetyltransferase in Saccharomyces cerevisiae During Fermentation. P. Malcorps, J. M. Cheval, S. Jamil, and J. P. Dufour, Unité de Brasserie et des Industries Alimentaires, Université Catholique de Louvain, Place Croix du Sud 2/Bte 7, B-1348 Louvain-la-Neuve, Belgium. J. Am. Soc. Brew. Chem. 49:0047, 1991.

The factors that influence ester synthesis were evaluated by measuring and comparing specific activities of in vivo and in vitro alcohol acetyltransferase (AAT) (EC 2.3.1.84) during different conditions of fermentation. The high specific rate of ester synthesis observed at the end of the growth phase is related to the induction of AAT rather than to increased availability of acetyl-coenzyme A. Induction of AAT is dependent on de novo protein synthesis and is "inhibited" by linoleic acid and oxygen. Such inhibition of the enzyme in vivo is not due to the modification of the physicochemical properties of the cellular membrane or to competitive inhibition, as previously suggested. Furthermore, the effect of oxygen and unsaturated fatty acid on ester synthesis cannot be related to a lesser availability of acetyl-coenzyme A. Results suggest that ester synthesis is modulated by a repression-induction of enzyme synthesis or processing, the regulator of which is presumably linked to yeast lipid metabolism. The same enzymatic system or common regulation mechanism is involved in the synthesis of both ethyl and acetic acid esters.

Keywords: Yeast, Esters, Alcohol acetyltransferase, Acetylcoenzyme A, Linoleic acid, Oxygen