RESUMO
The effects of melittin on the activities of Na+-K+-ATPase and glucose-6-phosphate dehydrogenase (G-6-PD) which are on the membrane of red blood cell (RBC) are chosen as the index of this study. The possible target sites of these effects through enzyme activity determination by spectrophotometry are investigated, and the hemolytic process and the activity change of these two types of enzymes on the RBC membrane are discussed. The results show that the main mode of melittin inhibition to the activity of enzymes on the RBC membrane is the coexistence of adhesion/insertion form and free-state form, and the effect of the former is more stronger than the latter. The K+ binding site of Na+-K+-ATPase is one of the target sites of melittin. The membrane-insertion process of melittin synchronizes with the action of melittin on this enzyme. Melittin slowly inhibits the catalysis of G-6-PD through the action on G-6-P and NADP, and the extent in which melittin forms tetramers isclosely related to the enzyme activity. EDTA inhibits the aggregation of melittin, and interferes with its action on G-6-P. The biochemical mechanisms of melittin effects on the substrate G-6-P and the coenzyme NADP are similar, and the inhibition of melittin is not related to the structure of G-6-PD.