Interaction between human IgG and human creatine kinase isoenzyme-1 in serum: a route for the intravascular catabolism of creatine kinase-1?

In vitro incubation, at 37 degrees C, of human creatine kinase isoenzyme-1 (isoenzyme BB) and human immunoglobulin G in a buffer results in the formation of a complex of high relative molecular mass (Mr approximately 825,000), which contains both proteins. This complex also forms in vitro if creatine kinase isoenzyme-1 is incubated with fresh human serum. The creatine kinase activity of the complex obtained from either incubation is extremely labile, even in the presence of a chelating agent and a thioglycerol. We present evidence for the existence of this complex in the sera of patients who have detectable serum creatine kinase isoenzyme-1 activity. Sera with high activities of creatine kinase isoenzyme-2 do not appear to have this complex. We therefore speculate that complexing of creatine kinase isoenzyme-1 with serum immunoglobulin G may be a pathway of enzyme degradation.