Kohashi M, Kasuya Y, Watanabe T
School of Food and Nutritional Sciences, University of Shizuoka, Yada, Japan.
Biosci Biotechnol Biochem. 1996 Feb;60(2):284-7. doi: 10.1271/bbb.60.284.
Non-thermal effects of a ceramics radiation on reversibility of lactate dehydrogenase reaction have been investigated using the enzyme irradiated on cooling, and a pyruvate/NADH (system I) or a lactate/NAD+ (system II) as substrate. The Km for lactate in the system II using the irradiated enzyme tended to decrease just like balancing with the increase in Km for pyruvate in system I. The Vmax/Km for system II was increased 2.3-fold by the 18-h irradiated enzyme. Each enthalpy and entropy change in system II using the 18-h irradiation of the enzyme was decreased by 21 kJ mol-1, although that in system I was increased by 12 kJ mol-1. From a thermodynamic analysis, it was estimated that solvation of the active center of LDH was promoted and stabilized by the irradiation, and that it caused this regulation of the reversibility of LDH.
利用冷却时辐照的酶以及丙酮酸/还原型辅酶Ⅰ（体系Ⅰ）或乳酸/辅酶Ⅰ（体系Ⅱ）作为底物，研究了陶瓷辐射对乳酸脱氢酶反应可逆性的非热效应。在体系Ⅱ中，使用辐照酶时乳酸的米氏常数（Km）趋于降低，这与体系Ⅰ中丙酮酸的Km增加相平衡。体系Ⅱ中使用辐照18小时的酶时，最大反应速率与米氏常数之比（Vmax/Km）增加了2.3倍。使用辐照18小时的酶时，体系Ⅱ中的焓变和熵变均降低了21kJ/mol，而体系Ⅰ中的则增加了12kJ/mol。通过热力学分析估计，辐照促进并稳定了乳酸脱氢酶活性中心的溶剂化作用，并导致了乳酸脱氢酶反应可逆性的这种调节。
