Energetics of the budding cycle of Saccharomyces cerevisiae during glucose limited aerobic growth

Summary

A method for the estimation of the yield on energy (Y _ATP) and of the efficiency of oxidative phosphorylation, in vivo (P/O ratio) is described, which is based on the measurement of effective gas exchange values ($Q_{O_2 }$ and $Q_{CO_2 }$) and of the yield coefficient Y of continuously growing populations of baker's yeast which vary in the degree of fermentation and respiration. For Y _ATP a value of 12.0±0.5 $\frac{{{\text{mg dry weight formed}}}}{{{\text{mMole ATP}}}}$ and for P/O ratio one of 1.1±0.05 $\frac{{{\text{mMole ATP}}}}{{{\text{1/2 mMole O}}_{\text{2}} }}$ was found and seems to be independent of the type of glucose catabolism (under glucose limitation).

The gas exchange of populations of Saccharomyces cerevisiae synchronized at different growth rates was determined. The specific oxygen uptake and carbon dioxide formation rate, Q _{O 2}, and Q _{CO 2}, are shown to depend on the state of the cells in the budding cycle. Increase in gas metabolism and therefore increased energy generation coincides with the initiation of budding. The longer the generation time g the more expressed are these oscillations of energy formation over the budding cycle. The relationship between the course of energy generation and energy storage and the sequence of budding and single cell phase over the division cycle is discussed.