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Isoforms of creatine kinase (CK) MM were analyzed in serum from normal subjects and patients with neuromuscular diseases using a specific monoclonal antibody. This specific antibody can inhibit the activity of the CK-M subunit containing lysine at the C-terminal residue, tissue-type CK-M, but does not inhibit the CK-M subunit that does not contain lysine at the C-terminal residue, serumtype CM-M. The change by muscle exercise of biochemical markers in serum was examined in healthy subjects and those with neuromuscular disease. Muscle exercise(mountain climbing) increased serum total CK to 2-5 times that before exercise. Tissue-type CK-M increased more than serum-type CK-M in serum obtained 3 hours after reaching the top of the mountain. In myogenic diseases, progressive muscular dystrophy had high total CK activity(6380±4263IU/I), and both tissue-type CK-M and serumtype CK-M were highly active, 2968±1962 and 3412±2301IU/1, respectively. Myotonic dystrophy and myopathy due to hypothyroidism also had high total CK activity. The rate of increase of tissue-type CK-M was greater than that of serum-type CK-M. The results indicate that tissue CK is continuously released into the blood stream due to muscle damage by diseases such as myogenic diseases. On the other, hand, a slight change of total CK was observed in neurogenic disease. Tissue-type CK-M increased more than seum-type CK-M, and was correlated with the clinical state. The combination of total CK and CK-MM isoform was considered to be a more sensitive marker than total CK, GOT(AST) or other biochemical markers for diagnosis of the stage of neuromuscular disease.
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