Location and activity of the respiratory enzymes of baker's yeast and brewer's bottom yeast grown under anaerobic and aerobic conditions.

SUMMARY: The activity of the electron-transport enzymes of baker's yeast or brewer's bottom yeast, grown under anaerobic conditions, was very low. When anaerobic baker's yeast was cultured aerobically to the mid-exponential phase with limited carbon source, the activity of the electron-transport enzymes increased 3- to 10-fold and, correspondingly, the activity in the stationary phase rose 10- to 50-fold. For brewer's bottom yeast the increase of activity induced by oxygen in the aerobic stationary phase was only about 3- to 4-fold and the activity was clearly lower than that of baker's yeast. The activity of the electron-transport enzymes accumulated in the 10,000 g sediment, which under aerobic conditions contained 60-80% of the total activity; the NADPH2 oxidase system formed an exception. The activity of the enzymes of the citric acid cycle also increased under aerobic conditions but only 2- to 10-fold in baker's yeast of the aerobic stationary phase; in brewer's bottom yeast the increase during oxygen adaptation was proportionally greater. The bulk of the enzymes of the citric acid cycle were found in the postmitochondrial supernatant, while the 10,000 g sediment contained 20 to 40% of the total activity. The 10,000 g sediment of anaerobically grown baker's yeast contained mitochondrial precursors, while the 10,000 g sediment from the aerobic exponential phase contained mitochondria with a more developed structure, showing a respiratory control ratio of 1.4-1.7 with several substrates. The internal structure of the mitochondria was not completely developed until the aerobic stationary phase, where the uptake of oxygen with several substrates also increased many fold.