An Investigation of the Metabolism of Valine to Isobutyl Alcohol in Saccharomyces cerevisiae

Abstract

The metabolism of valine to isobutyl alcohol in yeast was examined by 13 C nuclear magnetic resonance spectroscopy and combined gas chromatography-mass spectrometry. The product of valine transamination, ␣-ketoisovalerate, had four potential routes to isobutyl alcohol. The first, via branched-chain ␣-ketoacid dehydrogenase to isobutyryl-CoA is not required for the synthesis of isobutyl alcohol because abolition of branchedchain ␣-ketoacid dehydrogenase activity in an lpd1 disruption mutant did not prevent the formation of isobutyl alcohol. The second route, via pyruvate decarboxylase, is the one that is used because elimination of pyruvate decarboxylase activity in a pdc1 pdc5 pdc6 triple mutant virtually abolished isobutyl alcohol production. A third potential route involved ␣-ketoisovalerate reductase, but this had no role in the formation of isobutyl alcohol from ␣-hydroxyisovalerate because cell homogenates could not convert ␣-hydroxyisovalerate to isobutyl alcohol. The final possibility, use of the pyruvate decarboxylase-like enzyme encoded by YDL080c, seemed to be irrelevant, because a strain with a disruption in this gene produced wild-type levels of isobutyl alcohol. Thus there are major differences in the catabolism of leucine and valine to their respective "fusel" alcohols. Whereas in the catabolism of leucine to isoamyl alcohol the major route is via the decarboxylase encoded by YDL080c, any single isozyme of pyruvate decarboxylase is sufficient for the formation of isobutyl alcohol from valine. Finally, analysis of the 13 C-labeled products revealed that the pathways of valine catabolism and leucine biosynthesis share a common pool of ␣-ketoisovalerate.

The Combined Effects of Oxygen Supply Strategy, Inoculum Size and Temperature Profile on Very-High-Gravity Beer Fermentation by Saccharomyces cerevisiae

“…It should also be noted that the slightly elevated end of fermentation fusel levels observed in the trials conducted under optimized conditions are consistent with the observed increase in FAN consumption, as all of the fusels specified are by-products of the catabolic valine pathway from ␣-ketoisovaleric acid. 18,52 Overall, the key flavour metabolites were not negatively influenced by the altered process conditions. wort.…”

Biochemistry of apple aroma: A review

“…These aldehydes can be reduced to their corresponding branched alcohol (2-methyl-butanol, 3-methyl-butanol and 2-methyl-propanol) by action of the ADH enzyme, which uses NAD(P) + as a cofactor (30,140,143,145,147). The transformation of amino acids into alcohols is known as the Ehrlich pathway, in which the key enzymes are transaminases, decarboxylases and dehydrogenases (148).…”

“…The transformation of amino acids into alcohols is known as the Ehrlich pathway, in which the key enzymes are transaminases, decarboxylases and dehydrogenases (148). Branched aldehydes can also be oxidized to their corresponding branched fatt y acid (2-methyl-butanoic, 3-methyl-butanoic and 3-methyl-propanoic) by the action of aldehyde dehydrogenase (AldDH) (30,140,143,147), which uses NAD(P)H as a cofactor.…”

“…In the fi rst, 2-oxo acids can be converted into branched aldehydes (2-methyl-butanal, 3-methyl-butanal, and 2-methyl-propanal, for Ile, Leu and Val, respectively) by oxidative carboxylation by an α-keto acid decarboxylase enzyme (for example pyruvate decarboxylase, PDC) (18,30,140,142,143,147). These aldehydes can be reduced to their corresponding branched alcohol (2-methyl-butanol, 3-methyl-butanol and 2-methyl-propanol) by action of the ADH enzyme, which uses NAD(P) + as a cofactor (30,140,143,145,147).…”

Growth of the salt-tolerant yeast in microtiter plates: effects of NaCl, pH and temperature on growth and fusel alcohol production from branched-chain amino acids

“…K-Ketoisovalerate and K-keto-L-methylvalerate show similar patterns towards NaCl and pH as K-ketoisocaproate. Cross talk between catabolic and anabolic reactions of the branched-chain amino acid metabolism may explain the formation of the di¡erent keto acids and fusel alcohols, as described by Dickinson et al [6,7]. Van der Sluis [16] has not reported the accumulation of these K-keto acids, which are not derived from leucine.…”