Kinetics and activation energetics of death in Saccharomyces cerevisiae induced by sulfur dioxide

Publisher Website
Google Scholar
Abstract
Death of Saccharomyces cerevisiae induced by sulfur dioxide (K2S2O2 was used as the SO2 source) followed saturation kinetics. The enthalpy of activation of death was not affected by concentration over the range tested (5–150) mg/L of (K2S2O2 at pH 3.4) and averaged 3.6 × 104 cal/mol as compared with 8.5 × 104 cal/mol for ΔH‡ of thermal death. The entropy of activation of death was hyperbolic function of the sulfur dioxide concentration, extrapolated at zero concentration to ΔS0‡ = 36.8 cal mol−1 K−1 and tended to ΔΔSmax‡ = 13.2 cal mol−1 K−1 at saturating concentration, yielding a dis0sociation constant of 5.8 × 10−1 M sulfur dioxide. As was predicted from these results, In Kd (the specific rate of death induced by sulfur dioxide) was hyperbolic function of concentration under isothermic conditions and extrapolated toa finite value at zero concentration. The Arrhenuis plots and the ΔS± plot versus concentration revealed the occurrence of substrate inhabitation of the death effect at high concentrations (above 60 mg/L K2S2O2 at pH 3.4). A model is presented involving two types of receptor sites for sulfur dioxide on the cell surface, on directly connected with the death process, the other modulating its entropy of activation.