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

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.

Exploration of Sulfur Assimilation of Aspergillus fumigatus Reveals Biosynthesis of Sulfur-Containing Amino Acids as a Virulence Determinant

“…Interestingly, the sF⌬ strain was furthermore unable to grow on BSA as a source of sulfur and/or nitrogen. We previously showed that the assimilation of certain sulfur sources varies depending upon the availability of nitrogen (33); also, sulfite reductase activity is known to be affected by the nitrogen source (89). We therefore tested the growth capacity of the mutant on different nitrogen sources, which did not utilize BSA under any of the tested conditions.…”

Natural Abundance Isotopic Fractionation in the Fermentation Reaction: Influence of the Fermentation Medium

“…From the point of view of the yeast metabolism, pH 5.5 is considered as optimum. The role of nitrogen and phosphorus in fermentation reactions is well documented (11)(12)(13). The growth of microorganisms requires nitrogen, and phosphates are mechanistically involved in the reactions.…”

“…The initial concentration in nitrogenous nutrients in grape juices has also been shown to influence the production and activity of the biomass and the yield of the conversion of sugar into ethanol (15). It is considered that at least 140 mg liter Ϫ1 of assimilable nitrogen is required by the yeast to completely ferment 180 to 250 g liter Ϫ1 of grape sugar in the presence of at least 300 Ȑg liter Ϫ1 of phosphates (13,16). Since there is no simple connection between the isotopic effects of the medium and its influence on the reaction rate, we have attempted to identify the species mainly responsible for the variations in the isotopic Note.…”

“…The standard deviation on the isotopic determination is about 0.2‰ for 13 C and 0.5 ppm for 2 H. Nuclear magnetic resonance. The site-specific hydrogen isotope ratios of the methyl, I, and methylene, II, site of ethanol were determined by SNIF-NMR (8) using AM400 and AMX500 Bruker spectrometers equipped with 2 H ͕ 1 H͖ dedicated probes, internal 19 F locking devices, and automatic sample changers.…”

MET17and Hydrogen Sulfide Formation inSaccharomyces cerevisiae

“…One hypothesis is that low levels of reduced sulfur incorporation result in "leakiness" of reduced sulfur and subsequent release of H 2 S (16,19). Thus, strains that are high producers of H 2 S should have relatively low levels of OAS/OAH SHLase activity.…”