The mechanism of the formation of higher alcohols from amino acids by Saccharomyces cerevisiae

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Abstract
Dialyzed crude cell-free extracts of Saccharomyces cerevisiae catalyse the transfer of amino groups from aspartic acid, leucine, norleucine, isoleucine, valine, norvaline, methionine, phenylalanine, tyrosine and tryptophan to 2-oxoglutarate. The transamination of aspartic acid, phenylalanine, leucine, valine and tyrosine with 2-oxoglutarate is stimulated by the addition of pyridoxal phosphate. When leucine, norleucine, valine or norvaline is incubated with 2-oxoglutarate in the presence of extracts of S. cerevisiae, glutamate, CO2 and aldehyde are produced. Addition of pyridoxal phosphate to this system stimulates the rate of formation of CO2. 2-Oxoisovaleric acid, 2-oxovaleric acid, 2-oxoisocaproic acid and 2-oxocaproic acid are rapidly decarboxylated by both cell-free extracts and purified yeast carboxylase to give CO2 and their corresponding aldehydes. [rho]-Hydroxyphenylpyruvate is decarboxylated very slowly with large amounts of purified yeast carboxylase. Extracts oxidize reduced diphosphopyridine nucleotide on the addition of [rho]-hydroxyphenylacetaldehyde, butyraldehyde, isobutyraldehyde, valeraldehyde or isovaleraldehyde. Crystalline alcohol dehydrogenase also behaved in a similar manner. The rate of reduction decreased with increasing length of C chain. The mechanism proposed for the conversion of tyrosine into tyrosol appears to be a general one for the formation of all the constituents of fusel oils.