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  • Title: [Effect of pH on Ca-binding properties of calmodulin and on its interaction with Ca-dependent phosphodiesterase of cyclic nucleotides].
    Author: Tkachuk VA, Men'shikov MIu.
    Journal: Biokhimiia; 1981 Jun; 46(6):963-73. PubMed ID: 6266519.
    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).
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