A macro creatine kinase isoenzyme in serum of apparently healthy individuals.

Activity of creatine kinase B subunit, as measured by an immunoinhibition assay, is persistently increased in certain healthy, asymptomatic adults, whose values for total CK activity are within normal limits. Serum samples from two such individuals were investigated by electrophoresis, heat inactivation, determination of activation energies, and immunosorption (on protein A). The results demonstrated the presence of a circulating complex of IgG and CK-BB, which has been described as macro CK, type I. To our knowledge, this is the first report of such macro CK isoenzymes in healthy individuals.