Quantitation of creatine kinase isoenzymes in human tissues and sera by an immunological method.

Antisera against the crystallized creatine kinase isoenzymes from human skeletal muscle (MM) and from human brain (BB) were produced in rabbits. Both the MM and BB isoenzymes were precipitated quantitatively by their homologous antisera. No cross-reaction was observed. Thy hybrid MB from human heart muscle could not be precipitated completely by either of the two antisera. In artificial mixtures the concentrations of individual creatine kinase isoenzymes were determined from the percentage of non-precipitable activity in the supernatant after reaction with each of the antisera. This immunotitration assay was applied to study the quantitative distribution of creatine kinase compared with those determined by electrophoretic analysis. In sera of patients with myocardial infarction, the immunotitration assay allowed the sensitive and rapid quantitation of creatine kinase isoenzymes, especially of the "infarct-specific" hybrid MB, even in sera with low total activity. This indicates that the method is of diagnostic value.