The control of mitochondrial enzyme synthesis in yeast: A new hypothesis

It has been well documented that either an excess of glucose or a lack of oxygen [I] causes respiration to cease in the facultative anaerobe, Saccharomyces cerevisiae. This ‘repression’ phenomena is characterized by a decrease in mitochondrial enzyme activity which is closely coupled to a loss in mitochondrial profiles [ 21. It has been strongly suggested by a number of investigators [3-51 that the concentration of glucose alone determined whether these cells will be regimented into an anaerobic or aerobic type of metabolism. The experiments reported here show that it is possible to differentiate between repression due to anaerobiosis from that due to carbon source. A possible system of this control is discussed. Yeast were grown aerobically to mid exponential fermentative phase in a medium and manner described previously [6]. The harvested cells which were strongly repressed when transferred from glucose and slightly repressed when transferred from galactose (i.e., an excess of hexose still present in each culture medium) (cf. [7] ), were used to inoculate a second batch of medium in the manner described in table 1. At various times after transfer, dry weight, respiratory ability, malic dehydrogenase (MDH) and cytochrome c oxidase (cyt. oxidase) activities of the yeast were determined. The respiratory ability which was determined polarographically on isolated culture samples aerated for one minute prior to measurement, reflected the oxidative capability of the yeast cell in the culture at the time of sampling. Since yeast utilize glucose and galactose at different rates the results of these experiments are expressed in terms of activity versus change in dry weight in order