Determination of SULT1A1 activity in human tissues by PNPS assay method.
The β-Naphthol sulfation activity was determined from the tumor tissue and its surrounding. This assay determines phenol sulfation activities of different isoforms of phenol sulphating SULTs. A reaction mixture containing 50mM Tris buffer, pH 6.2, 5mM PNPS, 20 M PAPS, and 0.1mM -naphthol was used to measure the sulfation activity. Tumor and surrounding tissue cytosols (50 μg protein) were used as the enzyme source in a total reaction volume of 250 μl. After 30 min incubation at 37ºC in a shaking water bath, the reaction was stopped by adding 250μl of 0.25M Tris, pH 8.7. The reaction mixtures were read at 401 nm in a spectrophotometer. Specific activity (SA) was expressed as nmole/minute/mg of protein (22).