Studies on the Mechanism of the Inhibitory Action of Zephiran on Yeast Cells

Abstract

At 1:1,000 or higher concs. of zephiran, the absorption bands of a prepn. of cytochrome c, and of yeast cells, are either markedly faded or abolished. In manometric measurements, in a 1:35,000 dilution of zephiran, the O2 consumption of p-phenylenediamine in yeast cells was completely inhibited. Under similar conditions the aerobic and anaerobic oxidation of glucose by yeast cells was likewise inhibited by zephiran. In the presence of 1.8% serum proteins these inhibitions were counteracted, showing that yeast and serum proteins compete for zephiran. The competition can be* expressed as follows: (protein: :: zephiran) protein + zephiran + yeast (zephiran:::yeast). The final dilution figures adopted as a measure of the efficacy of zephiran against a given living cell are very impressive. They may, however, prove misleading. An analysis on a wt. to wt. basis yields a ratio which is remarkablv small. A 1:55,000 dilution of zephiran, found to be inhibitory for the growth of yeast cells, on a wt. to wt. basis shows a ratio (mg. yeast to mg. zephiran) of only 15:1. Similarly, the wt. ratio of a 1:220,000 dilution of zephiran is only 65:1. In the presence of 1.8% serum proteins, at least a 4-fold greater amt. of zephiran is required. In studies which attempt to establish a correlation of the inhibition of oxygen consumption with the inhibition of growth it is necessary a) that the cells being tested be principally dependent for growth on the utilization of O2, or b) that the utilization of O2 markedly renders inactive other respiratory processes which do not utilize O2. The results of studies which deal with the inhibition of O2 consumption in yeast or bacterial cells, in simple buffer substrate systems, do not appear to be always adequate to define the nature of the inhibitions of the growth-promoting metabolic processes which are not related in the main to the O2-consuming systems. Metabolic processes involving amino acids, in which dehydrogenation reactions take place through the intermediary functions of various H acceptors, without the utilization of O2, are growth-supporting processes. The measurement of O2 alone failed to give information regarding these processes. Absence of the inhibition of O2 consumption in the presence of growth should not therefore be interpreted as indicating that the inhibition of growth is not related to the inhibition of oxidative enzyme processes, since O2 is only one of the numerous H acceptors participating in oxidation reduction processes.