SUMMARY: After growth in a medium containing 2% (w/v) galactose, a strain of showed greater oxidative activity, an essentially unchanged anaerobic fermentation rate and an increase in total growth, compared with yeast grown in the same medium but containing instead 2% (w/v) glucose as major carbon source. The galactose-grown yeast possessed a generally higher level of oxidative metabolism, with enhanced values (up to 500%) with glucose and other oxidizable substrates, a higher cytochrome content and a greatly increased cytochrome oxidase activity. These differences were associated with an inhibitory effect of glucose on the formation of cxidative enzymes when this sugar was present in the growth medium at concentration greater than 0·05% (w/v). Changes in the composition of the basal growth medium greatly altered the magnitude of the differences between the glucose-grown and galactose-grown organisms and the differences were not apparent with certain growth media. Possible interpretations of these findings are discussed.


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