Human CK-MB is composed of two subunits, CK-M and CK-B which both have
an active site. With the aid of specific antibodies to CK-M, the catalytic activity
of CK-M subunits in the sample is inhibited to 99.6 % without affecting the
CK-B subunits. The remaining CK-B activity, corresponding to half the CK-MB
activity, is determined by the total CK method. As the CK-BB isoenzyme
only rarely appears in serum and the catalytic activity of the CK-M and CK-B
subunits hardly differ, the catalytic activity of the CK-MB isoenzyme can be
calculated from the measured CK-B activity by multiplying the result by 2.