The use of the Barcroft apparatus for the measurement of tissue respiration

THE RATE OF OXYGEN UTILIZATION BY YEAST AS RELATED TO TEMPERATURE

Suspensions of the yeast Saccharomyces cerevisiae gave reproducible rates of O(2) uptake over a period of 6 months. The relation of rate of consumption of O(2) to temperature was tested over a wide range of temperatures, and the constant in the formulation of the relationship is found to be reproducible. The values of this constant (micro) have been obtained for five separate series of experiments by three methods of estimation. The variability of micro has the following magnitudes: the average deviation of a single determination expressed as per cent of the mean is +/-2 per cent in the range 30-15 degrees , and +/-0.8 per cent in the range 15-3 degrees C. This constancy of metabolic activity measured as a function of temperature can then be utilized for more precise investigations of processes controlling the velocity of oxidations of substrates, and of respiratory systems controlled by intracellular respiratory pigments. The data plotted according to the Arrhemus equation give average values of the constant micro as follows: for the range 35-30 degrees , micro = 8,290; 30-15 degrees , micro = 12,440 +/-290; 15-3 degrees , micro = 19,530 +/-154. The critical temperatures are at 29.0 degrees and 15.7 degrees C. A close similarity exists between these temperature characteristics (micro) and values in the series usually obtained for respiratory activities in other organisms. This fact supports the view that a common system of processes controls the velocities of physiological activities in yeast and in other organisms.

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.