Metabolism of Endothelium-Derived Relaxing Factor, Nitric Oxide, by Glutathione S-Transferases

(1)人谷胱甘肽s -转移酶-pi （GST-pi）和GST-mu活性受到鸟苷酸环化酶激活剂血卟啉的剂量依赖性抑制。对GST-pi和GST-mu具有50%抑制活性（IC_<50>）的人卟啉浓度分别为14.2和2.2 muM。硝普苷是一种释放一氧化氮（NO）的化合物，对GST-pi、GST-mu和gst - α活性有抑制作用，其IC_<50>值为0.04 ~ 0.14 muM。亚硝酸盐（NO_2）对GST-pi和gst - α活性无抑制作用，但对GST-mu活性有抑制作用，IC_<50>值为0.39 muM。由于硝酸甘油在Mu类GST形式下的Km值为1.1-2.5 muM，这些酶从硝酸甘油中释放的亚硝酸盐可能抑制了它们的活性。(2)大肠杆菌中表达的重组大鼠GST-P可结合血红素。此外，与未表达GST-P的大肠杆菌相比，表达GST-P的大肠杆菌对过氧化氢处理更敏感，过氧化氢酶和其他几种er蛋白的表达减少。(3)利用半胱氨酸残基被丙氨酸独立取代的GST-P突变体进行的定点诱变实验表明，过氧化氢的失活主要是由于第47和101个半胱氨酸残基之间形成了二硫键。由于所有突变体都具有与野生型相似的特异活性，因此这4个半胱氨酸残基中没有一个是GST-P活性所必需的，但第47和101个半胱氨酸残基可能位于谷胱甘肽结合的重要区域，这些残基之间形成二硫键导致空间位阻。这些突变体还表明，n -乙基马来酰亚胺的失活是由于sh试剂与第47个半胱氨酸残基的结合。(4)研究了过氧化物酶体增殖剂和x射线照射对Pi类GST表达的影响。已知这两种处理都能诱导活性氧的产生，导致这些形式的表达受到抑制。少

(1) The activities of human glutathione S-transferase-pi (GST-pi) and GST-mu were dose-dependently inhibited by hematoporphyrin, an activator of guanylate cyclase. The concentrations of humatoporphyrin to give a 50% inhibition of activity (IC_<50>) were 14,2 muM for GST-pi and 2.2 muM for GST-mu. Nitroprusside, a compound to release nitric oxide (NO), inhibited the activities of GST-pi, GST-mu, and GST-alpha, IC_<50> values of nitroprusside being 0.04 - 0.14 muM.Nitrite (NO_2) did not inhibit the activities of GST-pi or GST-alpha, but inhibited GST-mu activity, with an IC_<50> value of 0.39 muM.Since the Km values for nitroglycerin are 1.1-2.5 muM in Mu class GST forms, nitrite released from nitroglycerin by these enzymes is suggested to inhibit their activities.(2) Recombinant rat GST-P expressed in Escherichia coli was shown to bind heme. Furthermore, E.coli expressing GST-P were more sensitive to hydrogen peroxide treatment and exibited reduced expression of catalase and several oth … More er proteins than E.coli not expressing GST-P.(3) Experiments utilizing GST-P mutants whose cysteine residues were independently substituted with alanine by site-directed mutagenesis revealed that inactivation by hydrogen peroxide was mainly due to disulfide bond formation between the 47th and 101st cysteine residues. Since all mutants have similar specific activities to that of the wild type, none of the four cysteine residues is essential for GST-P activity but the 47th and 101st cysteine residues may be located in an important region for glutathione binding, disulfide bond formation between these residues resulting in steric hindrance. These mutants also revealed that inactivation by N-ethylmaleimide was due to the binding of the SH-reagent to the 47th cysteine residue.(4) The effects of peroxisome proliferator administration and x-ray irradiation on expression of Pi class GST forms were investigated. Both treatments, known to induce the procuction of active oxygen species, resulted in the repressed expression of these forms. Less