An immunologic pathway for intravascular catabolism of creatine kinase subform MM3.
In vitro incubation of the MM3 subform of human creatine kinase (ATP:creatine N-phosphotransferase, EC 2.7.3.2, CK) with fresh human serum resulted in the formation of a complex of high relative molecular mass (Mr 320 kDa). The formed complex (macro CK-MM3) consists of both CK-MM3 and immunoglobulin A (IgA), and its amount of the formed complex was proportional to CK-MM3 activity and IgA concentration. Two molecules of CK-MM3 combined with one molecule of IgA, and the immunoglobulin inhibited the enzyme activity. As IgA does not form complexes with other subforms (CK-MM2 and CK-MM1) or CK-MB, the antigen specificity of IgA to CK-MM3 is definitely exacting. The circumstantial evidence suggests that macro CK-MM3 is a specific antigen-antibody complex. Macro CK-MM3 was detected in all of the examined sera of adult patients with more than 2001 U/1 CK activity (the positive percentage of macro CK-MM3 in all adult patients was 73%), but not detected in sera of patients who were younger than 12 months old. No relationship was observed between macro CK-MM3 and the patients' underlying diseases. Macro CK-MM3 formation suggested to be an immunologic pathway for intravascular catabolism of CK-MM3 when its activity increases.
Kanemitsu
F
F
Department of Clinical Chemistry, Kurashiki Central Hospital, Japan.
Okigaki
T
T
D000293:Adolescent; D000328:Adult; D000368:Aged; D000936:Antigen-Antibody Complex / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D003402:Creatine Kinase / Q000276:immunology*; D000939:Epitopes / Q000276:immunology; D006801:Humans; D007070:Immunoglobulin A / Q000378:metabolism*; D007223:Infant; D007231:Infant, Newborn; D007525:Isoelectric Focusing; D007527:Isoenzymes; D008875:Middle Aged; D009132:Muscles / Q000201:enzymology*
D000936:Antigen-Antibody Complex; D000939:Epitopes; D007070:Immunoglobulin A; D007527:Isoenzymes; D003402:Creatine Kinase