ToxSci Advance Access originally published online on November 9, 2005
Toxicological Sciences 2006 89(2):438-443; doi:10.1093/toxsci/kfj037
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Genetic Analysis of Glutathione S-transferase A1 Polymorphism in the Chinese Population and the Influence of Genotype on Enzymatic Properties1
* Department of Pharmacology, Basic Medical College of Wuhan University, Wuhan 430071, China; and Department of General Surgery, Zhongnan Hospital of Wuhan University, Wuhan 430071, China
Received September 14, 2005; accepted November 2, 2005
Genetic polymorphisms of human glutathione S-transferases (hGSTs) have important implications for drug efficacy and cancer susceptibility. hGSTA1 is the most abundant subfamily of hGSTs. The aim of this study was to investigate the distribution of hGSTA1 genetic polymorphism in the Chinese population and whether there exists the potential activity alterations caused by this polymorphism. Therefore, genomic DNA was extracted from peripheral blood of 140 healthy Chinese people and 11 normal liver tissues obtained from patients who had undergone liver surgery. Two variants in the promoter region of the hGSTA1 gene were identified by polymerase chain reaction-restricted fragment length polymorphism (PCR-RFLP). Activities toward selected substrates of the wild type (hGSTA1*A) and variant (hGSTA1*B) were measured spectrometrically using S-9 fractions from liver samples. 
5-androstene-3,17-dione (AD), cumene hydroperoxide (CuOOH), and 1-chloro-2,4-dinitrobenzene (CDNB) were used as marker substrates toward hGSTA1, hGSTA, and hGST, respectively. The kinetic parameters (Km, Vmax, and Vmax/Km) of hGSTA1 were determined with different concentrations of AD. The results showed that, in the study population, the proportions of hGSTA1*A/*A, hGSTA1*A/*B, and hGSTA1*B/*B genotypes were 75.0, 24.3, and 0.7%, respectively, and the allele frequencies of hGSTA1*A and hGSTA1*B were detected to be 87.1 and 12.9%, respectively. The variant hGSTA1 showed a significantly decreased activity for AD isomerization as compared to the wild type. Kinetic analyses revealed that the Vmax value of the variant hGSTA1 was 48% of that of the wild type despite a Km value of 62% (p < 0.01). This means that the Vmax/Km in the variant hGSTA1 was 76%. These data indicate that the distribution of hGSTA1 gene is polymorphic in Chinese and is different from those in other racial populations. The promoter sequence polymorphism of the hGSTA1 gene is associated with decreased Km and Vmax values of the enzyme in individuals with the variant allele. This variant is also associated with a decrease in hGSTA1 activity toward preferred substrates. This altered activity, however, is accompanied by significant individual variation in the variant population.
Key Words: glutathione S-transferases; polymorphism; promoter; catalytic activity; enzyme kinetics.