Volume 6, Number 4, p.p. 155-157
Catalytic activity of yeast alcohol dehydrogenase in water-sugar solutions
Abdol-Khalegh Bordbar,1,* Mehran Miroliaei2 and Venus Ravanmehr1
1 Laboratory of Biophysical Chemistry, Department of Chemistry, Isfahan University, Isfahan 81746-73441, Iran
2 Department of Biology, University of Isfahan, Isfahan 81746-73441, Iran
The catalytic activity of native and apo-yeast alcohol dehydrogenase (YADH) in water-sugar solutions has been investigated experimentally. The effect of sugars such as sucrose and trehalose and the influence of polyols such as mannitol and sorbitol were evaluated based on the residual enzyme activity at various substrate (ethanol) concentrations, in 50 mM phosphate buffer, pH 7.8 and 25 ºC. The catalytic efficiency (Kcat/Km) of both forms of the enzyme was calculated from the corresponding Michaelis-Menten plots. Apo-YADH, which lacks structural zinc, showed a significantly higher efficiency than the native enzyme. While sorbitol provided a slight enhancement in holo-YADH activity, the other sugar solutions alleviated this parameter slightly. The effect of sugar osmolytes on the kinetic parameters of the apo enzyme was investigated and it was found that its residual activity significantly increased in the following order: trehalose > sucrose > sorbitol > mannitol. Interpretation of the results was based on the molecular mechanism of sugars as solvoactivator agents and attributed to the structure-function relationship in YADH.
Keywords:
catalytic efficiency, polyols, solvoactivation of enzymes, sugars, yeast alcohol dehydrogenase