title: Differential effects of compound 48/80 on the ATPase and phosphatase activities of the Ca2+ pump of red cells.
abstract: The calmodulin antagonist compound 48/80 inhibits the phosphatase activity of the Ca2+-ATPase lowering its maximum velocity and leaving unaltered its apparent affinity for the substrate regardless on whether phosphatase activity is elicited by Ca2+ plus ATP or by calmodulin. Compound 48/80 has no effect on the Ki for ATP as inhibitor of the phosphatase. These results contrast sharply with the large increase that compound 48/80 induces in the apparent affinity of the regulatory site for the nucleotide of the Ca2+-ATPase and suggest that the active site for phosphatase activity is different from the regulatory site for ATP of the Ca2+-ATPase.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000328:Adult; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors* / Q000097:blood; D004912:Erythrocytes / Q000201:enzymology*; D006801:Humans; D007700:Kinetics; D009596:Nitrophenols / Q000378:metabolism; D009943:Organophosphorus Compounds / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors* / Q000097:blood; D003189:p-Methoxy-N-methylphenethylamine / Q000494:pharmacology*
chemical_list: D009596:Nitrophenols; D009943:Organophosphorus Compounds; C008644:nitrophenylphosphate; D003189:p-Methoxy-N-methylphenethylamine; D000255:Adenosine Triphosphate; D010744:Phosphoric Monoester Hydrolases; D000252:Calcium-Transporting ATPases; D002118:Calcium