Hydrogen sulphide production was examined in four strains of Saccharomyces cerevisiae. Hydrogen sulphide was formed in peaks of activity, coincident with the cessation of exponential yeast growth, and with depletion of an available nitrogen source in the medium. Hydrogen sulphide formation could be terminated by further additions of a nitrogen source. Addition of cycloheximide or iodoacetamide to exponentially growing cultures also caused hydrogen sulphide production and cessation of exponential growth. By terminating yeast growth at different stages, a peak of hydrogen sulphide producing activity was obtained which was similar to NADPH-sulphite reductase activity measured throughout exponential growth. Hydrogen sulphide was formed by reduction of bound sulphite present in the medium. Sulphite was transported, separately from the carbonyl components of bound sulphite, probably by diffusion. The toxicity of sulphite was studied in Saccharomyces cerevisiae and Saccharomycodes ludwigii. Sulphite transport into both yeasts was by diffusion although aspects of the transport superficially imitated active transport. The effects of sulphite upon amino-acid and glucose transport were examined in Saccharomyces cerevisiae. The action of sulphite upon respiration and fermentation of cells of Saccharomyces cerevisiae, differed between anaerobic and aerobic cells. This was discussed in terms of an uncoupling of glycolysis from high energy phosphorylation and the acidification of the interior of cells brought about by sulphite transport. Saccharomycodes ludwigii was resistant to ten fold greater concentrations of sulphite than Saccharomyces cerevisiae. This resistance can be explained by the low rate of transport of sulphite into Saccharomycodes ludwigii.
|Date of Award||1983|