Inter-individual variation of normal and Down syndrome glutathione transferase in response to different phenolic compounds.

Glutathione transferase (GST) catalyzes the conjugation of reduced glutathione (GSH) with a variety of xenobiotic compounds. Down syndrome (DS) considered as the most mental retardation genetic cause. GST was purified from the erythrocyte of two subjects subjected to genotype analysis normal (GSTT1(+)) and DS (GSTT1(+)& GSTM1(+)) erythrocytes by affinity chromatography. The effect of some bioactive compounds, eight different plant extracts and the daily supplement curcumin on the activity of GSTP from normal and DS was examined. Normal and DS GSTs were found to be different, 1) clove extract has inhibitory effect on normal GST (IC50 value of 3.63 mu g), while has no effect on DS GST. Eugenol (the clove major component) has no effect on normal and DS GSTs. 2) Tannic acid and quercetin have no effects on normal GST while they inhibit DS GST activity. Allyl-isthiocynate was not the most effective compound on DS GST activity (IC50 = 7.66 mu M). Tannic acid was 4.35 fold powerful inhibitor of DS GST activity (IC50 = 1.76 mu M) than allyl-isthiocynate. 2.5 mu g of rocket extract (the most effective plant on DS GST activity) caused decrease in the Km and Vmax values from 2 to 0.19 mM and from 50 and 10 mu moles / mm ri / mg protein, respectively, for glutathione substrate. While Vmax value was unchanged (20 mu moles / min / mg protein) with a Km equal 0.105 mM increased to 0.5 mM for CDNB.