Relation of Oxygen Tension and Temperature to the Time of Reduction of Cytochrome

The time for the appearance of the cytochrome C absorption band after shaking a suspension of bakers' yeast with various O(2)-N(2) mixtures was determined at each of six temperatures. At each temperature a linear relation between this interval-called the reduction time-and O(2) tension was found. It was shown: 1. That under our experimental conditions, absorption bands of cytochrome were seen when the O(2) tension of the suspension was reduced to, or below, a certain pressure which was found to be specific for each temperature (this pressure is provisionally considered to be identical with or very near to the "critical O(2) tension" usually found in Q(O(O2) )-O(2)-tension relationships); 2. That the x-axis intercept obtained from the reduction time - O(2)-tension plot gives the value of the "critical" O(2) pressure at each temperature; 3. That the O(2) tension within the suspension is reduced by the respiratory activity of the yeast cells. An equation describing these observations is given and is used in calculating rates of O(2) consumption from measurements of reduction time of cytochrome. The average difference between the calculated values and the manometric measurements of Q(O(O2) ) was found to be 6.6 per cent. A rapid optical method of measuring rates of O(2) consumption based on the findings of these experiments is proposed for use with cytochrome-containing microorganisms.