GSTA4, also known as glutathione S-transferase A4, belongs to the GST superfamily. This enzyme is involved in cellular defense against toxic, carcinogenic, and pharmacologically active electrophilic compounds. GSTA4 shows very high activity with reactive carbonyl compounds such as alk-2-enals. GSTA4 is highly effective in catalyzing the conjugate addition of reduced glutathione to 4-hydroxynonenal, an important product of peroxidative degradation of arachidonic acid and a commonly used biomarker for oxidative damage in tissue. This enzyme is expressed at a high level in brain, placenta, and skeletal muscle and much lower in lung and liver. Recombinant human GSTA4 protein, fused to His-tag at N-terminus, was expressed in E.Coli and purified