Melatonin is known to influence a variety of biological processes including circadian rhythms, neuroendocrine, and cardiovascular and immune functions as well as thermoregulation. Melatonin is the chief secretory product of the pineal gland, although it is also produced in other organs. In this study, in vitro effects of melatonin on 6-phosphogluconate dehydrogenase from human erythrocytes and in vivo effects of melatonin on 6-phosphogluconate dehydrogenase from rat (Sprague-Dawley) erythrocytes were studied. Human erythrocyte 6-phosphogluconate dehydrogenase was purified in 3 steps, namely haemolysate preparation, ammonium sulphate fractionation (35-65%) and 2´,5´-ADP Sepharose-4B affinity gel chromatography. 6-Phosphogluconate dehydrogenase was purified with a recovery rate of 88.8%, 2254-fold. Enzyme activity was spectrophotometrically measured using Beutler&#8217;s method. In addition, 6-phosphogluconate dehydrogenase activity was inhibited in vitro by melatonin. For the in vivo study, 16 adult male Sprague-Dawley rats weighing 200-250 g were used. The animals were divided into 2 equal groups of 8 animals each: the control and melatonin-treated groups. Both groups were kept under special conditions for 6 h. Melatonin at a 10 mg/kg pharmacological dosage also inhibited the enzyme significantly (P < 0.05) for 3 h invivo. However, enzyme activity increased to the normal level at 6 h.

Melatonin is known to influence a variety of biological processes including circadian rhythms, neuroendocrine, and cardiovascular and immune functions as well as thermoregulation. Melatonin is the chief secretory product of the pineal gland, although it is also produced in other organs. In this study, in vitro effects of melatonin on 6-phosphogluconate dehydrogenase from human erythrocytes and in vivo effects of melatonin on 6-phosphogluconate dehydrogenase from rat (Sprague-Dawley) erythrocytes were studied. Human erythrocyte 6-phosphogluconate dehydrogenase was purified in 3 steps, namely haemolysate preparation, ammonium sulphate fractionation (35-65%) and 2´,5´-ADP Sepharose-4B affinity gel chromatography. 6-Phosphogluconate dehydrogenase was purified with a recovery rate of 88.8%, 2254-fold. Enzyme activity was spectrophotometrically measured using Beutler&#8217;s method. In addition, 6-phosphogluconate dehydrogenase activity was inhibited in vitro by melatonin. For the in vivo study, 16 adult male Sprague-Dawley rats weighing 200-250 g were used. The animals were divided into 2 equal groups of 8 animals each: the control and melatonin-treated groups. Both groups were kept under special conditions for 6 h. Melatonin at a 10 mg/kg pharmacological dosage also inhibited the enzyme significantly (P < 0.05) for 3 h invivo. However, enzyme activity increased to the normal level at 6 h.