title: Hydrophobic regions function in calmodulin-enzyme(s) interactions.
abstract: Certain naturally occurring lipids (phosphatidylinositol, phosphatidylserine, arachidonic acid) and sodium dodecyl sulfate activate at least two calmodulin-dependent enzymes, bovine brain 3':5'-cyclic nucleotide phosphodiesterase and chicken gizzard myosin light chain kinase in the absence of Ca2+. 2-p-Toluidinyl-naphthalene-6-sulfonate (TNS), which is often used as a probe for hydrophobic groups of proteins, inhibits these two calmodulin-dependent enzymes. Kinetic analysis of inhibition of chicken gizzard myosin kinase by TNS revealed a competitive fashion against calmodulin-induced activation. The interaction between TNS and purified bovine brain calmodulin as demonstrated in the appearance of TNS fluorescence in the presence of 3 microM or more of calcium ion was not observed in the presence of 2 mM EGTA. This suggests that TNS is able to bind to calmodulin in the presence of Ca2+. Moreover, a calmodulin-interacting agent N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide suppressed the TNS fluorescence induced by complex formation with calmodulin in the presence of Ca2+. These results suggest that when Ca2+ binds to the high affinity sites of calmodulin, it induces a conformational change which exposes hydrophobic groups, and the calmodulin is then capable of activating calmodulin-dependent enzymes. We propose that hydrophobic properties of Ca2+-calmodulin are important for the activation of Ca2+-calmodulin-dependent enzymes.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology; D002118:Calcium / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology*; D002417:Cattle; D002645:Chickens; D004789:Enzyme Activation; D005895:Gizzard, Avian / Q000201:enzymology; D007700:Kinetics; D009218:Myosins / Q000378:metabolism*; D009282:Naphthalenesulfonates; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D011485:Protein Binding; D013050:Spectrometry, Fluorescence
chemical_list: D002135:Calcium-Binding Proteins; D002147:Calmodulin; D009282:Naphthalenesulfonates; C009497:2-(4-toluidino)-6-naphthalenesulfonic acid; D010727:Phosphoric Diester Hydrolases; D000251:Adenosine Triphosphatases; D009218:Myosins; D002118:Calcium