Regarding Creatine kinase (AIIMS May 2014)
Assertion: CK –MB is used for diagnosing MI
Reason: Cardiac muscle contain more CK-MB than CK-MM
|A||Both Assertion and Reason are true, and Reason is the correct explanation for Assertion|
|B||Both Assertion and Reason are true but Reason is not the correct explanation for Assertion|
|C||Assertion is true but Reason is false|
|D||Reason is true but Assertion is false|
a. Clinically, creatine kinase is assayed in blood tests as a marker of myocardial infarction (heart attack), rhabdomyolysis (severe muscle breakdown), muscular dystrophy, the autoimmune myositides and in acute renal failure. In the cells, the "cytosolic" CK enzymes consist of two subunits, which can be either B (brain type) or M (muscle type).
b. There are, therefore, three different isoenzymes: CK-MM, CK-BB and CK-MB.
i. CK-BB is expressed in all tissues at low levels and has little clinical relevance.
ii. Skeletal muscle expresses CK-MM (98%) and low levels of CK-MB (1%).
iii. The myocardium (heart muscle), in contrast, expresses CK-MM at 70% and CK-MB at 25–30%.