Creatine Kinase: Stability, Inactivation, Reactivation

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Abstract
I determined the in vitro biological half-lives or decay constants for creatine kinase isoenzymes at various temperatures. Values at 37 °C are consistent with values reported by others in vivo, which suggests that in vivo ir¬reversible inactivation is primarily thermal. Reversible inactivation appears to be an oxidation-reduction phe¬nomenon. Proteins and some inactivators (urate, cate¬cholamines) retard irreversible inactivation and preserve isoenzyme integrity. Dilution and thiols promote reversal of inactivity. Mercaptoethanol is the preferred thiol, par¬ticularly for storage and reactivation of isoenzyme MB. MB is sensitive to light and to freeze-thawing. I recommend that specimens be cooled promptly after drawing, that mercaptoethanol (10 mmol/liter) be added, and that they be stored refrigerated. Avoid prolonged exposure to light and freezing. A model of inactivation is proposed, which is based on the assumed existence of four monomer types: active, denatured, oxidized, and insulated. The model is consistent with dilution and thiol reactivation, lag phase variations, and subtype heterogeneity.