Studies on the Origin of Yeast Mitochondria

The mitochondria of aerobically grown yeast, in common with those of higher organisms, contain the terminal electron transport, oxidative phosphorylation, and citric acid cycle enzymes of the cell (9). However, unlike higher organisms, the yeast cell is capable of both aerobic and anaerobic growth, and, as was reported some years ago, the b and a cytochromes are not synthesized in the absence of oxygen but are adaptive enzymes formed in response to the presence of oxygen (2, 7). This communicat ion compares some of the cytology and enzymology of the yeast Torulopsis utilis grown both aerobically and anaerobically. I t is shown that, indeed, none of the respiratory chain cytochromes normally associated with the mitochondrial matrix are synthesized by T. utilis grown under strictly anaerobic conditions and that such cells contain no mitochondria but a new previously undescribed membrane system which contains some of the enzymes normally found in mitochondria. It appears that these membranes are concerned with the morphogenesis of mitochondria.