In this study, some enzymology parameters and some antibiotics affecting the enzyme activity of 6phosphogluconate dehydrogenase (6PGD) extracted from t the livers of fish from Lake Van (Chalcalburmas tarichi) were investigated because it is an important enzyme-producing NADPH, a reductive power, protecting the cell against the oxidative agents by producing reduced glutathione. The crude enzyme solution was obtained by using the affinity chromatography method. The native molecular weight of the enzyme is similar to 90,000 +/- 3000 Da and it is composed of two subunits with identical molecular weights of similar to 46,000 Da as exhibited on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The pH and temperature for optimal conditions of 6PGD were about 8.5 and 40 degrees C, respectively, and the enzyme showed optimal activity in 40 mM ammonium sulfate solution. In addition, in vitro effects of clindamycin phosphate, streptomycin sulfate, and lincomycin antibiotics on the enzyme activity were investigated.