Determination of sulphite reductase activity and its response to assimilable nitrogen status in a commercial Saccharomyces cerevisiae wine yeast

Jiranek, V., Langridge, P. and Henschke, P. A. (1996) Determination of sulphite reductase activity and its response to assimilable nitrogen status in a commercial Saccharomyces cerevisiae wine yeast. Journal of Applied Bacteriology, 81 (3), 329-336. (doi:10.1111/j.1365-2672.1996.tb04335.x).

Abstract

The liberation of H₂S is a common problem afflicting wine fermentation. Sulphite reductase activity of a commercial wine yeast was investigated to define its involvement in this process. The activity studied here differed from those characterized previously from cider and bakers' yeasts by displaying a greater sensitivity to cold, low ionic strength and possibly, proteolytic action. These differences necessitated the development of a new method of quantification. Through this method, the onset of H₂S liberation was shown not to be a result of variations in the levels of sulphite reductase activity. Thus, high levels of activity which occurred during the exponential phase of growth were not necessarily accompanied by the liberation of H₂S. Similarly, nitrogen-starved cultures which liberated H₂S showed no corresponding increase in sulphite reductase activity from prestarvation levels. In fact, rates of H₂S liberation from cultures and in enzyme assays agreed closely. A short-term independence of sulphite reductase activity from culture nitrogen status was therefore evident. The only influence of nitrogen was achieved in its absence when enzyme activity decayed with a half-life (4.25 h) which was comparable to that induced by the presence of cycloheximide (5.75 h). A proposed transcriptional control mechanism mediated by methionine derivatives was only partly effective in this strain although an in vitro inhibitory effect of methionine was implicated. These data therefore support the notion that H₂S liberation in response to nitrogen starvation stems from a failure of metabolism to sequester H₂S which continues to be formed, at least initially, at prestarvation rates.

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Contributors

Author: V. Jiranek

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