Formation of Higher Alcohols From14c-Labelled Valine and Leucine

The formation of isobutanol and 3-methylbutanol during alcoholic fermentation by brewer's yeast has been studied by adding uniformly 14C-labelled valine and leucine to the complex amino acid mixture which is used as nitrogen source. In the presence of 14C-leucine, only 3-methylbutanol becomes radioactive whereas, in the presence of 14C-valine, both isobutanol and 3-methylbutanol acquire label. The specific radioactivity of these compounds is, in all cases, inferior to that of the parent amino acids showing that a part of these higher alcohols is always formed by the synthetic functions of the yeast. The results suggest that the regulating effect of the valine and leucine level of the medium on the synthesis of these amino acids in yeast cells is rather limited. They furthermore indicate that intact assimilation of amino acids is not the only mode of their utilization, even in media with excessive levels of amino acids. An attempt is made to explain the dependence of the anabolic and catabolic modes of higher alcohol formation upon the nitrogenous nutrient level of the medium. The presence of radioactive isoleucine as impurity in the 14C-leucine used has allowed an approximative calculation of the formation of 2-methylbutanol from isoleucine which is very similar to the formation of isobutanol from valine.