A Kinetic Analysis of the Endogenous Respiration of Bakers' Yeast

The process of endogenous respiration of two strains of bakers' yeast, Saccharomyces cerevisiae, was examined kinetically. The rate of respiration with respect to time in a non-nutrient medium was found to exhibit two phases: (a) a period of constant rate of O(2) consumption and CO(2) production (R.Q. = 1) characteristic of cells with ample concentrations of stored material; (b) a first order decline in rate of respiration with respect to time, where the rate was proportional to the concentration of some substrate, S. (R.Q. = 1 throughout second phase.) The nature of this substrate was reexamined and the evidence summarized confirms the notion that it is a carbohydrate, probably glycogen. These phases of endogenous respiration were shown to depend upon the age of the culture and the amount of substrate available.