Stability of Macro Creatine Kinases and Creatine Kinase Isoenzymes Compared: Heat Inactivation Test for Determination of Thermostable Creatine Kinases

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Abstract
Creatine kinase isoenzymes showed decreasing thermal stability and increasing lability towards pH changes in the order: MM, MB and BB. The 3 isoenzymes exhibited their highest stability between pH 6.5-7.0. At 37.degree. C and an almost physiological pH of 7.5 the decay constants were 0.025, 0.164, and 0.580 h-1 (MM, MB and BB isoenzyme), respectively. In contrast to free creatine kinase BB, Ig-linked creatine kinase BB (macro creatine kinase BB, type 1 macro creatine kinase) showed a markedly higher stability; this accounts for the persistence of creatine kinase BB activity in macro creatine kinasemia. In addition a 2nd type of macro creatine kinase was identified in patients'' sera, which is also thermostable. A simple heat inactivation test (20 min, 45.degree. C, immunoinhibition of the M-subunits) differentiates thermostable macro creatine kinases from thermolabile creatine kinases and thus completes isoenzyme diagnosis.

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