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Creatine kinase. Modification of the working enzyme
The Biochemical Journal
|July 1, 1976
Summary
Creatine kinase enzyme protection against iodoacetamide inhibition was studied. Substrate mixtures and specific complexes offered significant protection, suggesting enzyme conformation changes during the reaction pathway.
Area of Science:
- Biochemistry
- Enzymology
Background:
- Creatine kinase (EC 2.7.3.2) catalyzes the reversible transfer of a phosphoryl group.
- Iodoacetamide is a known inhibitor of creatine kinase.
Purpose of the Study:
- To investigate the protective effects of substrates and reaction intermediates against iodoacetamide inhibition of creatine kinase.
- To correlate enzyme protection with conformational states relevant to the catalytic mechanism.
Main Methods:
- Enzyme inhibition assays using iodoacetamide.
- Kinetic analysis of creatine kinase inhibition rate constants.
- Varying substrate concentrations to determine protection levels.
Main Results:
- Substrate mixtures at near-saturating concentrations provided significant protection (up to 80%) against iodoacetamide.
- The complex of creatine-NO3--MgADP fully protected the enzyme, unlike its individual components.
- Protection levels correlated with enzyme conformation, particularly states resembling the creatine-PO3-MgADP intermediate.
Conclusions:
- Enzyme conformation plays a critical role in protection against iodoacetamide inhibition.
- The findings support the hypothesis that specific enzyme-bound intermediates, like creatine-PO3-MgADP, stabilize a conformation resistant to inhibition.