The inactivation profile of rabbit muscle creatine phosphokinase (CPK) has been investigated in Tris-acetate buffer solutions under various conditions of pH and temperature.
The inactivation pattern follows apparent first-order kinetics at pH very close to 6.00 (isoelectric point of CPK) and 30 to 39oC and at pH 7.40, 39oC. The activation energy of the inactivation at pH very close to 6.00 is 31.8 kcal/mol. The inactivation half-lives of CPK are 13.6h (pH 5.95, 30℃), 7.9h (pH 5.93, 35℃), 3.0h (pH 5.90, 39℃) and 11.9h (pH 7.40, 39℃).
.It pH 6.70, the inactivation profile follows a biexponential curve at 30℃ and at 39℃. The time course consists of two types of inactivation: an initial rapid inactivation (α-phase) and a gradual inactivation (β-phase).
Anomalous irregular inactivation profiles are also observed at pH 7.00, 7.40 and 8.00 at 30oC as well as at pH 8.00 at 3YoC. Some possible explanations of these irregular inactivation profiles are presented.