Régulation des alcool‐déshydrogénases chez Saccharomyces cerevisiae

Cell free preparation of a strain of Saccharomyces cerevisiae “adapted” to hydrocarbons catalyse the dehydrogenation of higher alcohols in the presence of NAD. Before the activity could be studied, it was necessary to develop a method for assaying it in heterogeneous media. The dehydrogenation of higher alcohols by these crude extracts in the presence of NAD is significant only when the alcohol emulsions are stabilized with Tween 80. We have shown using emulsions of varying fineness, that the affinity of the responsible enzyme for its substrates increases with diminishing particle size. The K m s for 1‐octanol emulsified into particles 2,1 μ and 0,1 μ in diameter are of the order of 1,8 × 10 −3 M and 0,4 × 10 −3 M, respectively. The enzyme is distinct from the classical ethanol dehydrogenase. It differs essentially in substrate specificity, in substrate affinity, in its insensivity to cyanide and azide and in temperature sensitivity. The two activities in a mixture can be distinguished by their kinetics at heat inactivation at 51°. The enzyme described here has different properties from those of the oxidative alcohol dehydrogenase studied by Schrimpfessel and Wiame. There is thus a heterogeneity of alcohol dehydrogenases in this yeast. Our assay which differentiates between two alcohol dehydrogenases synthesized by S. cerevisiae (ethanol dehydrogenase and octanol dehydrogenase) made it possible to determine enzyme levels as a function of culture conditions. It was demonstrated that both oxygen and substrates exert a regulatory effect. The octanol dehydrogenase is subject to a glucose effect and the ethanol dehydrogenase is absent from cells grown on n ‐tetradecane. Interest in the use of hydrocarbons lies essentially in their effect on ethanol dehydrogenase and in the selection of “adapted” cells which permit a study of octanol dehydrogenase.