ACTIVITY OF 4 ALLELIC FORMS OF GLUTATHIONE-S-TRANSFERASE HGSTP1-1 FORDIOL EPOXIDES OF POLYCYCLIC AROMATIC-HYDROCARBONS

Allelic forms of hGSTP1-1 which differ from each other by their cataly tic properties and, structurally, by the amino ac:id(s) in position(s) 104 or (and) 113 are known to exist in human populations. The four po ssible isoforms of hGSTP1-1 with isoleucine or valine in position 104 and with alanine or valine in position 113 were produced by site-direc ted mutagenesis of the cDNA followed by bacterial expression and purif ication of the proteins. Glutathione-conjugating activity was measured with the diol epoxides of benzo(a)pyrene and chrysene, as well as wit h the model substrate 1-chloro-2,4-dinitrobenzene. Isoenzymes with val ine in position 104 were more effective with the diol epoxides of poly cyclic aromatic hydrocarbons but less effective with 1-chloro-2,4-dini trobenzene than the iso forms with isoleucine 104. In addition, the tr ansition A113V in the presence of V104 caused a pronounced increase in catalytic efficiency for the benzo(a)pyrene but not the chrysene diol epoxide. It is proposed that amino acid 113 functions as part of a cl amp that lines the mouth of the water channel leading to the active si tes of the hGSTP1-1 dimer and controls the access to substrates. There fore, the hydrophobicity and the size of residue 113 are important in co-determining the substrate specificity of the isoenzymes. The widely different activities of the allelic isoforms toward carcinogenic diol epoxides of polycyclic aromatic hydrocarbons may help to explain the correlation between cancer susceptibility and genotype at the hGSTP1 l ocus that has been found by others. (C) 1997 Academic Press.