Chemical Properties
This is an off-white, salt-free lyophilized powder, soluble in water, with an optimal pH of 6.0-7.0 (forward reaction) and 9.0 (reverse reaction). Stability: Inactivated at a pH below 5, and thawing and freezing also inactivate the enzyme. At -20°C and a pH of 6.6, it is stable in 0.1 molar mass/L imidazole buffer for four weeks. It is most stable in a neutral 60% ethanol solution. Adding 0.1% albumin or β-mercaptoethanol to dilute solutions can increase stability. The freeze-dried product can be stored for 12 months at -20°C, but loses 15% activity after six months at 4°C. Inhibitors include para-chloromercuric benzoate, chelating agents, iodoacetic acid, tripolyphosphate, adenosine, nitrite, sulfate, bromide, sulfite, chloride, fluoride, thyroxine, 3,5-dinitro-o-cresol, coenzyme I (NAD), L-triiodoformyl amino acid (T3), malonate, iodine (I-), iodoacetic acid, orthophosphoric acid, pyrophosphate, and tripolyphosphate. Activators include Mg2+, Mn2+, 2-mercaptoethanol, dithiothreitol, glutathione, and the thiol N-acetylcysteine. The absorbance coefficient of a 1% aqueous solution at 280 nm is 8.76. The enzyme reaction is: creatine + adenosine triphosphate = adenosine diphosphate + creatine phosphate.
Biochem/physiol Actions
Creatine kinase plays a key role in the energy metabolism of cells with intermittently high and fluctuating energy requirements. Examples of such cells include cardiac or skeletal muscle cells and neural tissues of brain and retina. The enzyme catalyzes the reversible transfer of the phosphoryl group from phosphorylcreatine to ADP, in order to generate ATP. The molecular mass of the protein is found to be approximately 80,000 Da. It is made up of 2 subunits, each having a molecular weight of 40,000 ± 2000. The lighter subunit is present in larger amounts.
