title: A derivative of bisbenzylisoquinoline alkaloid is a new and potential calmodulin antagonist.
abstract: A new derivative of bisbenzylisoquinoline (berbamine type): 0-(4-ethoxylbutyl) berbamine (EBB) was found to possess powerful and specific calmodulin (CaM) inhibitory properties. It inhibited CaM-stimulated Ca2+-Mg2+-ATPase in human erythrocyte membrane with IC50 value of 0.35 microM compared to that of 60 microM of berbamine. CaM-independent basal Ca2+-Mg2+-ATPase, Na+-K+-ATPase and Mg2+-ATPase were not effect at 1.0 microM of EBB at which CaM-dependent Ca2+-Mg2+-ATPase was already potently inhibited. The inhibition of CaM-dependent Ca2+-Mg2+-ATPase was competitive with respect to CaM. Higher amount of CaM reversed the inhibition caused by higher concentration of EBB. Using dansyl-CaM (D-CaM), it was shown that EBB binds directly to CaM and caused a conformational change of CaM polypeptide chain. From fluorescence titration curve we obtained evidence that in the presence of Ca2+, CaM has two specific binding sites for EBB and additional unspecific binding sites. The Ca2+-dependent binding sites of EBB on CaM were novel region different from the binding sites for TFP.
mesh_terms: D000470:Alkaloids / Q000494:pharmacology*; D044182:Benzylisoquinolines; D001665:Binding Sites; D017301:Ca(2+) Mg(2+)-ATPase / Q000032:analysis; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000032:analysis; D002147:Calmodulin / Q000037:antagonists & inhibitors*; D004910:Erythrocyte Membrane / Q000032:analysis; D005453:Fluorescence; D006801:Humans; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis
chemical_list: D000470:Alkaloids; D044182:Benzylisoquinolines; D002147:Calmodulin; C050387:O-(4-ethoxybutyl)berbamine; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium; C027870:berbamine