The Pasteur effect in normal yeast and its inhibition by various agents

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Abstract
For the quantitative expression of that aspect of the Pasteur effect which consists of a lowering by oxygen of the rate of glucose utilization, the term Pasteur quotient (P.Q.) is proposed: P.Q. = QO2 Glucose / QN2 Glucose. The value of P.Q. in baker''s yeast at medium glucose concentrations is 0.2-0.25 when expressed in terms of glucose catabolized, and 0.5-0.6 in terms of total glucose utilized. At high glucose concentrations the P.Q. rises from 0.2 to 0.4, through the appearance of aerobic fermentation. The rate of glucose breakdown and polysaccharide synthesis, aerobically and anaerobically, are reported. Of the many substances which inhibit the Pasteur effect in some mammalian cells, only 2 classes also inhibit it in yeast: nitrophenols, and lower alphatic nitriles and isonitriles. The action of these 2 groups of substances differ in the following respects: 2,4-dinitrophenol (DNP) increases the amount of glucose catabolized aerobically above that catabolized anaerobically, i.e., P.Q. >1.0; propionitrile never increases the P.Q. about 1.0; DNP entirely inhibits polysaccharide synthesis aerobically, . propionitrile does not. The bearing of these results on the mechanism of the Pasteur effect is discussed.