Location and Activity of the Respiratory Enzymes of Baker's Yeast and Brewer's Bottom Yeast Grown under Anaerobic and Aerobic Conditions

Abstract

SUMMARYThe 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 yo of the total activity ; the NADPHz 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 I 0,000 g sediment from the aerobic exponential phase contained mitochondria with a more developed structure, showing a respiratory control ratio of I '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.

Variations in the Localization of Acetyl-Coenzyme A Synthetase in Aerobic Yeast Cells

“…To test more critically whether the integrity of the mitochondria had been significantly reduced by the procedures used here, tests were performed for NADP-isocitrate dehydrogenase. This enzyme has a bimodal distribution in S. cerevisiae (17,18), and Perlman and Mahler, using sphaeroplast preparations, have shown that about 15% of the total found in yeast homogenates is clearly local-ized in the mitochondria (18). In a series of assays for this enzyme, we found a similar bimodal distribution between the soluble and mitochondrial fractions, the latter accounting for 12 to 20% of the total.…”