Creatine kinase distribution

The selection of which enzyme to measure in serum for diagnostic or prognostic purposes depends on a number of factors. An important factor is the distribution of enzymes among the various tissues, shown, for example, for aspartate aminotransferase, alanine aminotransferase, and creatine kinase in Figure 8-14. The main enzymes of established clinical value, together with their tissues of origin and their major clinical applications, are listed in Table 8-3 (see also Chapter 21). 

The diagnosis of organ disease is aided by measurement of a number of enzymes characteristic of that tissue or organ. Most tissues have characteristic enzyme patterns (Table 8-2) that may be reflected in the relative serum concentrations of the respective enzymes in disease. The diseased tissue can be further identified by determination of the isoenzyme pattern of one of these enzymes (e.g., lactate dehydrogenase, creatine kinase) in the serum, since many tissues have characteristic isoenzyme distribution patterns for a given enzyme. For example, creatine kinase (CK) is a dimer composed of two subunits, M (for muscle) and B (for brain), that occur in three isoenzyme forms, BB(CKi), MB(CK2) and MM(CK3), which catalyze the reversible phosphorylation of creatine with adenosine triphosphate (ATP) as the phosphate donor ... 

Magnesium is closely associated with calciiun and phosphorus. About 70 per cent of the total magnesium is found in the skeleton but the remainder, which is distributed in the soft tissues and fluids, is of crucial importance to the well-being of the animal. Magnesium is the commonest enzyme activator, for example in systems with thiamin pyrophosphate as a cofactor, and oxidative phosphorylation is reduced in magnesium deficiency. Magnesium is an essential activator of phosphate transferases (e.g. creatine kinase) and it activates pyruvate carboxylase, pyruvate oxidase and reactions of the tricarboxylic acid cycle therefore, it is essential for the... 

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