Effects of some drugs on human erythrocyte 6-phosphogluconate dehydrogenase: an in vitro study

The inhibitory effects of some drugs on 6-phosphogluconate dehydrogenase from human erythrocytes have been investigated. For this purpose, initially, erythrocyte 6-phosphogluconate dehydrogenase was purified 3364 times in a yield of 58% by using ammonium sulfate precipitation and 2', 5'-ADP Sepharose 4B affinity gel. A temperature of + 4 degrees C was maintained during the purification process. Enzyme activity was determined with the Beutler method by using a spectrophotometer at 340 nm. This method was utilized for all kinetic studies. Many commonly used drugs were investigated in this study. Some drugs (ketotifen (K-i : 8.3 +/- 1.7 mu M), dacarbazine (K-i : 10.1 +/- 0.7 mu M), meloxicam (K-i : 50.9 +/- 13.2 mu M), furosemide (K-i : 127 +/- 37.8 mu M), methotrexate (K-i : 136.7 +/- 25.3 mu M), metochloropramide hydrochloride (K-i : 2.1113 +/- 0.6979 mM), ritodrine hydrochloride (K-i : 6.0353 +/- 1.2783 mM), and gadopentetic acid (K-i : 73.4 +/- 21.9 mM)) inhibited enzyme activity in vitro. K-i constants for the enzyme were found by means of Lineweaver-Burk graphs. All drugs showed non-competitive inhibition. In addition, IC50 values of the drugs were determined by plotting activity percent vs [I].