title: [Effect of pH on Ca-binding properties of calmodulin and on its interaction with Ca-dependent phosphodiesterase of cyclic nucleotides].
abstract: The fluorescence of dansyl immobilized on bovine brain calmodulin is sensitive to Ca2+. This effect is due to Ca2+ attachment to specific Ca2+-binding sites of calmodulin and is maintained within a wide range of pH. The native and dansyl-modified calmodulin preparations exert similar activating effects on Ca-dependent phosphodiesterase of cyclic nucleotides and have practically the same affinity for the enzyme. Using fluorescence measurements of the calmodulin--dansyl conjugate, it was shown that the decrease of pH from 9.0 down to 6.0 gradually decreases the constant of Ca2+ binding to calmodulin from 1.5 . 10(10) M-1 to 1.6 . 10(6) M-1. This decrease of pH does not affect the calmodulin affinity for phosphodiesterase. The activating effect of calmodulin on phosphodiesterase is more pronounced at acidic pH values (6.0-7.0) than at alkaline pH values (8.0-9.0).
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002417:Cattle; D003619:Dansyl Compounds / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D011485:Protein Binding
chemical_list: D002135:Calcium-Binding Proteins; D002147:Calmodulin; D003619:Dansyl Compounds; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D002118:Calcium
vernacular_title: Vliianie pH na Ca-sviazyvaiushchie svoistva kal'modulina i na ego vzaimodeĭstvie s Ca-zavisimoĭ formoĭ fosfodiésterazy tsiklicheskikh nukleotidov.