Keen J H, Habig W H, Jakoby W B
J Biol Chem. 1976 Oct 25;251(20):6183-8.
The catalyzed reactions of GSH with organic nitrate and thiocyanate esters and with a series of chloronitrobenzene substrates have been investigated and the results used to formulate a mechanism for glutathione S-transferase catalysis. All the homogeneous preparations of the glutathione transferases that have been tested catalyze the reaction of GSH with organic nitrates and thiocyanates. The nature of the reaction with nitrate esters, resulting in the formation of GSSG rather than a thioether, has been investigated further. The presence of an additional nonsubstrate thiol decreased the formation of GSSG to an extent that cannot be explained by disulfide interchange. These results are interpreted to reflect the enzymatic formation of an unstable glutathione sulfenyl nitrite that undergoes subsequent non-enzymatic decomposition. Hammett plots of the catalytic constants of rat liver transferases B and C obtained with a series of 4-substituted 1-chloro-2-nitrobenzene substrates demonstrate a linear relationship with sigma- substituent constants, reflecting the nucleophilic nature of the enzymatic reactions and their strong dependence on the electrophilicity of the nonthiol substrate. These data suggest that the many diverse reactions catalyzed by the glutathione transferases may be formulated as a nucleophilic attack of enzyme-bound GSH on the electrophilic center of the second substrate. The final products observed reflect this primary event and the existence of subsequent nonenzymatic reactions.
已对谷胱甘肽（GSH）与有机硝酸盐、硫氰酸酯以及一系列氯硝基苯底物的催化反应进行了研究，并利用这些结果阐述了谷胱甘肽S-转移酶催化作用的机制。所有经过测试的谷胱甘肽转移酶均相制剂都能催化GSH与有机硝酸盐和硫氰酸盐的反应。对于与硝酸酯的反应性质，该反应导致生成谷胱甘肽二硫化物（GSSG）而非硫醚，已进行了进一步研究。额外非底物硫醇的存在使GSSG的生成量减少，其减少程度无法用二硫键交换来解释。这些结果被解释为反映了不稳定的谷胱甘肽亚磺酰亚硝酸盐的酶促形成，随后该物质会发生非酶促分解。用一系列4-取代的1-氯-2-硝基苯底物获得的大鼠肝脏转移酶B和C催化常数的哈米特图显示，其与σ-取代常数呈线性关系，这反映了酶促反应的亲核性质及其对非硫醇底物亲电性的强烈依赖性。这些数据表明，谷胱甘肽转移酶催化的许多不同反应可能可表述为酶结合的GSH对第二种底物亲电中心的亲核攻击。观察到的最终产物反映了这一主要事件以及随后非酶促反应的存在。
