title: Proton nuclear magnetic resonance studies on the kinetics of tryptic fragments of calmodulin upon calcium binding.
abstract: The kinetics of the Ca2+-dependent conformational change of the tryptic fragments F12 (residues 1-75) and F34 (residues 78-148) of calmodulin were studied by 1H-NMR. Resonances of two phenylalanines, 16 (or 19) and 65 (or 68), N epsilon, N epsilon, N epsilon-trimethyllysine-115 and tyrosine-138 were examined by the saturation-transfer technique or computer-aided line-shape simulation to obtain the rate of the conformational exchange between the Ca2+-free form and the Ca2+-bound form. The rates for F12 and F34 in the presence of 0.2 M KCl at 22 degrees C were 300-500 s-1 and 3-10 s-1, respectively. Activation parameters are as follows: Delta H not equal to = 11(+/- 2) kcal X M-1 and delta S not equal to = -9(+/- 5) cal X K-1 X M-1 for F12, and delta H not equal to = 16(+/- 2) kcal X M-1 and delta S not equal to = -2(+/- 5) cal X K-1 X M-1 for F34. These kinetic data for the conformational exchange are in agreement with those of Ca2+ dissociation from the binding sites obtained by 43Ca-NMR and stopped-flow fluorescence studies.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D007700:Kinetics; D008239:Lysine / Q000031:analogs & derivatives; D009682:Magnetic Resonance Spectroscopy; D008974:Mollusca; D010446:Peptide Fragments; D010649:Phenylalanine; D011487:Protein Conformation; D014357:Trypsin; D014443:Tyrosine
chemical_list: D002147:Calmodulin; D010446:Peptide Fragments; C003712:trimethyllysine; D014443:Tyrosine; D010649:Phenylalanine; D014357:Trypsin; D008239:Lysine; D002118:Calcium