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

p-Hydroxyphenylacetaldehyde + reduced DPN + p-Hydroxyphenylethanol (tyrosol) + oxidized DPN (3) In reaction (1), the removal of the amino group is effected by transamination; 2-oxoglutarate was found to be essential for this step. This is followed by decarboxylation of the keto acid (reaction 2) to yield the aldehyde, which is reduced in the third stage to give the alcohol. In the first investigation, tyrosine was chosen as a substrate because of the relative ease with which the intermediates and the product could be estimated (SentheShanmuganathan & Elsden, 1958). Many other amino acids give rise to fusel oils, and, having established the pathway of tyrosol formation, it was desirable to extend the work in order to decide whether other fusel oils were formed by a similar mechanism. This paper describes these investigations. In experiments with growing cultures and whole cells, where glucose is an essential component, ethanol was always formed in addition to the alcohol corresponding to the amino acid added as substrate. The presence of ethanol made the estimation of other alcohols difficult. The cell-free extracts used would not reduce added aldehyde in the absence of a hydrogen donor and the amino acid is only converted as far as the corresponding aldehyde containing one less carbon atom than the parent compound. Moreover, there is no formation of ethanol by unrelated reactions or by endogenous metabolism. Consequently, the work reported in this paper has been done with cell-free extracts.