An all-ornone response in thh release of potassium by yeast cells with methylene blue and other basic redox dyes

Basic redox dyes, such as methylene blue, induce a loss of K⁺ from yeast cells. The maximal loss, rather than the rate of loss, is related to the dye concentration, the response following a normal distribution on a plot of log-dose, versus percentage loss of K⁺. This fact taken together with the observed correlation between K⁺ loss and frequency of staining (as measured by microscopic observation), indicates that the response is all-or-none for individual cells. The response is produced by all the basic redox dyes tested (9), but by none of the acidic dyes (4). However, only the oxidized form of the dye is effective. Cations protect the cells from the basic dyes in a competitive manner, the bivalent cations (especially UO₂⁺⁺) being more effective than monovalent cations. It is suggested that the action of the dyes involves two steps, the first a binding to ribonucleic acid in the cell membrane (with competition from cations) and the second, an oxidation of neighboring sulfhydryl groups to the disulfide form. At a threshold level, unique for each cell, a generalized membrane breakdown occurs, resulting in the release of potassium and of other cytoplasmic constituents.

The induction by allyl glycine of heritable respiratory deficiency in Saccharomyces and its reversal by sulphur amino acids

Respiration-deficient mutants can be induced in populations of Saccharomyces growing in the presence of the cysteine antagonist, allyl glycine. Mutations occur, however, only among cells which had been cultivated anaerobically so as to be unadapted to aerobic respiration prior to exposure to the antagonist. The mutagenicity of allyl glycine is relieved by cysteine, and to a lesser extent by homocysteine, methionine, or alpha-amino-n-butyric acid. It is accentuated by homoserine. Evidence is presented indicating that the ability of allyl glycine to induce respiratory mutants is distinct from its general growth-inhibiting properties. It is concluded that the maintenance of the genetic determinant of respiration in Saccharomyces depends upon a particular metabolic function in which cysteine participates. In cells cultivated anaerobically that function is so limited that it can be rendered effectively inactive by growth in the presence of allyl glycine.