NAD-DEPENDENT AND NADP-DEPENDENT 11-BETA-HYDROXYSTEROID DEHYDROGENASEISOFORMS IN GUINEA-PIG KIDNEY WITH GOSSYPOL INHIBITION

AIM: To study the mechanism of gossypol-induced hypokalemia. METHODS: The 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) protein was pr epared from guinea pig kidney. The activity of 11 beta-OHSD with NAD o r NADP as the coenzyme was measured by HPLC in both control and gossyp ol treatment. RESULTS: The V-max and K-m were 0.64 mmol . h(-1)/g prot ein and 0.07 mu mol (cortisol) for NAD-dependent 11 beta-OHSD, 1.75 mm ol . h(-1)/g protein and 0.21 mu mol (cortisol) for NADP-dependent 11 beta-OHSD, respectively when 80 mu g of enzyme protein was used. The i nhibitory effects of gossypol on these two 11 beta-OHSD isoforms were different. The IC50 (95 % confidence limits) were 50.2 (48.3 - 52.0) m u mol of gossypol for NAD-dependent 11 beta-OHSD and 1143 (1098 - 1188 ) mu mol of gossypol for NADP-dependent 11 beta-OHSD. The K-i was goss ypol 96 mmol . L-1 for the former and 340 mmol . L-1 for the latter. C ONCLUSION: The NAD-dependent 11 beta-OHSD is a more critical physiolog ic mechanism than NADP-dependent 11 beta-OHSD for hypokalemia caused b y gossypol.