SUMMARY: The immediate effects of externally added alcohols on CO production and O consumption of suspensions of washed, aerated baker's yeast were studied by stopped-flow membrane inlet mass spectrometry. Glucose-supported fermentation was progressively inhibited by increasing ethanol concentration (0-20%, v/v). The inhibition by ethanol was quite different from that observed for acetaldehyde; thus it is unlikely that toxicity of the latter can account for the observed effects. For five different alkanols (methanol, ethanol, I-propanol, 2-propanol and I-butanol) increasing inhibition of anaerobic fermentation was correlated with increased partition coefficients into a hydrophobic milieu. This suggests that the action of ethanol is primarily located at a hydrophobic site, possibly at a membrane. Results for respiratory activities were not as definite as for those for anaerobic metabolism because some alkanols act as respiratory substrates as well as giving inhibitory effects.


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