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Effect of Temperature on the Uptake of 35S(-II) by Wine YeastsDepartment of Chemistry University of Auckland Private Bag Auckland, New Zealand
Department of Chemistry University of Auckland Private Bag Auckland, New Zealand
Department of Chemistry University of Auckland Private Bag Auckland, New Zealand
Department of Chemistry University of Auckland Private Bag Auckland, New Zealand The rates of uptake of 35S from S(-II) solutions by wine yeasts, Saccharomyces cerevisiae strains R92 and R104 and Saccharomyces chevalieri strain R93, were measured at pH 3.1 and 7.2 over the temperature range 5 ° C to 80 ° C and at 0.3 (or 0.5) mM and 5.0 mM S(-II) concentrations. Three critical temperatures were observed; the first, at ca 20 ° C is attributed to a phase change of the yeast cell membrane from a crystalline to a liquid crystalline state; the second, at the temperature of maximum activity at 30 ° C to 40 ° C is thought to arise from a switch from a metastable to a thermodynamically more stable state which is less effective in supporting the transport functions; and the third, at tempera tures greater than 50 ° C correlates well with the thermal viability of the yeasts. Variation of the activation energy, Ea, with extracellular S(-II) concen tration was observed and Ea for the uptake of S(-II) from a solution of 5 mM S(-II) at pH 7.2 was higher than at pH 3.1. The values of E a support the postulate of a simple diffusion of H2S(aq) and carrier mediated transport of HS-(aq) for the transport of S(-II).
Journal of Bioactive and Compatible Polymers, Vol. 1, No. 3,
335-347 (1986) |
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