Effects of melatonin on enzyme activities of glucose-6-phosphate dehydrogenase from human erythrocytes in vitro and from rat erythrocytes in vivo

The in vivo and in vitro effects of melatonin on glucose-6-phosphate dehydrogenase (G6PD) from human erythrocytes have been investigated. For this purpose, human erythrocyte glucose-6-phosphate dehydrogenase was purified, at the beginning, 13.654 times in a yield of 28% by using ammonium sulphate precipitation and 2',5'-ADP Sepharose 4B affinity gel. A temperature of +4 degreesC was maintained during the purification process. Enzyme activity was determined by the Beutler method using a spectrophotometer at 340 nm. This method was utilized for all kinetic studies. For in vitro experiments, the enzyme activity increased below 0.08 mM melatonin concentration and reached a plateau above 0.1 mM. Ten mg kg(-1) melatonin was administered intraperitonally and indicated the stimulatory effect on the enzyme. Time-dependent in vivo studies were executed for melatonin in Sprague-Dawley type rats. It was found that G6PD activity in the erythrocytes was increased by the melatonin in 1.5 and 3.5 h. These results show that both in vitro (below 0.08 mM) and in vivo pharmacological levels of melatonin increased enzyme activity in erythrocytes. The findings also indicate that melatonin may be pharmacologically useful in patients where a deficiency of the enzyme in red blood cells (RBC) causes haemolytic anaemia. (C) 2001 Academic Press.