Satoh K
Second Department of Biochemistry, Hirosaki University, School of Medicine, Japan.
Carcinogenesis. 1995 Apr;16(4):869-74. doi: 10.1093/carcin/16.4.869.
Enzymatic properties of five human glutathione S-transferases (GSTs) and non-enzymatic conjugation rates of GST substrates were examined as a function of glutathione (GSH) concentration and pH. GSTP1-1 showed a broad substrate specificity with both low and high GSH (10 mM) concentrations at pH 7.0, and the inhibitor insensitivity was then prominent. Among the GST substrates tested, ethacrynic acid, p-nitrophenylacetate, 1-chloro-2,4-dinitrobenzene and trans-4-phenyl-3-buten-2-one conjugated nonenzymatically with half-times of 0.39, 3.1, 9.4 and 10.0 min respectively at 10 mM GSH, pH 7.0 and 35 degrees C. The half-time for acrolein estimated by extrapolation was approximately 0.5 s. While the enzymatic reaction rates were independent of GSH at concentrations larger than Km values according to Michaelis-Menten kinetics and relatively insensitive to a pH change from 6.5 to 7.0, the non-enzymatic ones were linearly proportional to the GSH concentration and sensitive to pH. The enhanced non-enzymatic conjugation of various electrophiles at high GSH concentrations may in part account for the physiological significance of GSH elevation in preneoplastic and neoplastic cells.
研究了五种人谷胱甘肽S-转移酶（GSTs）的酶学性质以及GST底物的非酶促结合速率与谷胱甘肽（GSH）浓度和pH值的关系。GSTP1-1在pH 7.0时，对低浓度和高浓度（10 mM）的GSH均表现出广泛的底物特异性，且对抑制剂不敏感。在所测试的GST底物中，在10 mM GSH、pH 7.0和35℃条件下，依他尼酸、对硝基苯乙酸、1-氯-2,4-二硝基苯和反式-4-苯基-3-丁烯-2-酮的非酶促结合半衰期分别为0.39、3.1、9.4和10.0分钟。通过外推法估算的丙烯醛半衰期约为0.5秒。根据米氏动力学，当GSH浓度大于Km值时，酶促反应速率与GSH浓度无关，且对pH从6.5到7.0的变化相对不敏感，而非酶促反应速率与GSH浓度呈线性比例关系，且对pH敏感。在高GSH浓度下，各种亲电试剂非酶促结合的增强可能部分解释了GSH在肿瘤前和肿瘤细胞中升高的生理意义。
