Purification and Characterization of Glucose 6-Phosphate Dehydrogenase from Sheep Liver


Abstract: Glucose 6-phosphate dehydrogenase (D-glucose 6-phosphate: NADP^{+} oxidoreductase, EC; G6PD) was purified from sheep liver by a simple and rapid method. The purification process consisted of two steps: preparation of the homogenate, and 2', 5'-adenosine diphosphate (ADP) Sepharose 4B affinity chromatography. Through the use of these two consecutive steps, the enzyme was purified with a yield of 35.6% and 1,920 fold, having the specific activity of 11.2 enzyme units (EU/mg protein). A K_{M} of 0.176 mM and a V_{\max} of 0.0179 EU/ml were obtained for G6-P, and 0.0194 mM and 0.0223 EU/ml for NADP^{+}. Enzymatic activity was measured spectrophotometrically according to Beutler's method at 340 nm and optimal pH and assay temperature were determined. By means of a Lineweaver-Burk plot, the inhibitor constant for NADPH was determined to be K_{i}, 4.707 \pm 0.49 \mu M and it was shown to inhibit the enzyme in a non-competitive manner. The purification of enzyme was monitored by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (SDS-PAGE). SDS-PAGE showed a single band at \sim 55 kDa for the enzyme and gel filtration chromatography indicated it to be a dimer.

Keywords: Glucose 6-phosphate dehydrogenase, purification, sheep, liver

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