Singhal S S, Saxena M, Ahmad H, Awasthi S, Haque A K, Awasthi Y C
Department of Human Biological Chemistry and Genetics, University of Texas Medical Branch, Galveston 77555.
Arch Biochem Biophys. 1992 Dec;299(2):232-41. doi: 10.1016/0003-9861(92)90269-3.
Glutathione S-transferase (GST) isozymes of human lung have been purified, characterized, quantitated, and, based on their structural and immunological profiles, identified with their respective classes. The tau-, mu-, and alpha-class GSTs represented 94, 3, and 3% activities of total human lung GSTs toward CDNB, respectively, and 60, 10, and 30% of total GST protein, respectively. Both the mu- and the alpha-class GSTs of human lung exhibited heterogeneity. The two mu-class GSTs of human lung had pI values of 6.5 and 6.25 and were differentially expressed in humans. Significant differences were seen between the kinetic properties of these two isozymes and also between the lung and liver mu-class GSTs. The alpha-class GST isozymes of lung resolved into three peaks during isoelectric focusing corresponding to pI values of 9.2, 8.95, and 8.8. All three alpha-class GSTs isozymes had blocked N-termini and were immunologically similar to human liver alpha-class GSTs. Peptide fingerprints generated by SV-8 protease digestion and CNBr cleavage indicated minor structural differences between the liver and the lung alpha-class GSTs. The three alpha-class GSTs of lung expressed glutathione peroxidase activities toward the hydroperoxides of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylglycerol, with Km values in the range of 22 to 87 microM and Vmax values in the range of 67-120 mol/mol/min, indicating the involvement of the alpha-class GSTs in the protection mechanisms against peroxidation. All three classes of lung GSTs expressed activities toward leukotriene A4 methyl ester and epoxy stearic acid but the mu-class GSTs had relatively higher activities toward these substrates.
人肺谷胱甘肽S-转移酶（GST）同工酶已被纯化、表征、定量，并根据其结构和免疫特性确定了各自所属的类别。tau-、mu-和alpha-类GST分别占人肺总GST对1-氯-2,4-二硝基苯（CDNB）活性的94%、3%和3%，分别占总GST蛋白的60%、10%和30%。人肺的mu-类和alpha-类GST均表现出异质性。人肺的两种mu-类GST的等电点值分别为6.5和6.25，在人群中差异表达。这两种同工酶的动力学特性之间以及肺和肝mu-类GST之间均存在显著差异。肺的alpha-类GST同工酶在等电聚焦过程中分离为三个峰，对应等电点值分别为9.2、8.95和8.8。所有三种alpha-类GST同工酶的N端均被封闭，且在免疫上与人肝alpha-类GST相似。由SV-8蛋白酶消化和溴化氰裂解产生的肽指纹图谱表明肝和肺alpha-类GST之间存在微小的结构差异。肺的三种alpha-类GST对磷脂酰胆碱、磷脂酰乙醇胺和磷脂酰甘油的氢过氧化物表现出谷胱甘肽过氧化物酶活性，米氏常数（Km）值在22至87微摩尔范围内，最大反应速度（Vmax）值在67 - 120摩尔/摩尔/分钟范围内，表明alpha-类GST参与了抗过氧化的保护机制。所有三类肺GST对白三烯A4甲酯和环氧硬脂酸均表现出活性，但mu-类GST对这些底物的活性相对较高。
