Aerobic adaptation in yeast. II. Changes in enzyme profiles during a step-down anaerobic-aerobic transfer.

The levels of various enzymes and components of the glycolytic and respiratory pathways of the yeast Saccharomyces cerevisiae have been determined during a step-down, anaerobic-to-aerobic transition. These activities were determined as an adjunct to the respective metabolite data reported in the first paper in this series. It is clear from the data that anaerobic conditions induce an environment conducive to express glycolytic enzyme activities, while manifesting a differential induction/repression effect on oxidative enzymes. An NAD/NADH mediated mechanism is proposed to explain this difference. Of the enzymes assayed only cytochrome c oxidase shows any direct response to oxygen challenge and consequently it is suggested that the assembly of this enzyme is the trigger mechanism and rate-limiting step in aerobic adaptation.