Magnetic resonance studies on inactivated forms of creatine kinase.
نویسندگان
چکیده
Magnetic resonance and relative enzymatic velocity studies with the use of the paramagnetic manganese ion were carried out on creatine kinase inactivated by the specific -SH reagents iodoacetic acid and dinitrofluorobenzene and by the nonspecific reagents urea and decyl sulfate. Modification of creatine kinase at the two essential --SH groups by iodoacetic acid or dinitrofluorobenzene affected the enzymatic velocity, but had little, if any, effect on the binding constants or the environment at the binding sites of MnADP-, ADP3-, Mn-2’-dADP-, or Mn-ATP+, as determined from the enhancement of the relaxation rate of the water protons due to formation of ternary complexes of enzyme, manganese, and nucleotide. The addition of creatine to the ternary Mn-ADP-enzyme complex with the native enzyme caused a change in the proton relaxation rate measured over the temperature range, 2O-43’; as the temperature decreased the binding constant of Mn-ADP changed slightly, but the creatine-binding constant increased by a factor of about 30. The effect of creatine on the proton relaxation rate of water could be ascribed to a decreased rate of exchange of the manganese water ligands with the solvent water in the quaternary complex relative to the ternary complex and to a longer correlation time for the dipole-dipole interaction between manganese and water in the coordination sphere because of increased immobilization at the binding site of Mn-ADP. No such effect of creatine was observed for enzyme with the two essential cysteine residues carboxymethylated, indicating either that creatine is no longer bound to this form of the enzyme or that carboxymethylation of the essential -SH
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ورودعنوان ژورنال:
- The Journal of biological chemistry
دوره 243 10 شماره
صفحات -
تاریخ انتشار 1968