Several polymorphisms in the coding regions of the human GSTO1 have been identified. A polymorphism causing an alanine-to-aspartate (A140D) substitution in amino acid 140 produces a variant with lowered enzyme activities in the arsenic biotransformation.GSTO1 Variant Human Recombinant produced in E.Coli is single, a non-glycosylated, Polypeptide chain containing 241 amino acids fragment (1-241) having a total molecular mass of 36kDa and fused with a 4.5kDa amino-terminal hexahistidine tag. The GSTO1 is purified by proprietary chromatographic techniques.