To Measure Activity of Creatine Kinase
in Serum^33
33.1 Theory
Creatine kinase (CK), also called creatine phosphokinase, exists as three
isoenzymes, i.e., CK 1 ,CK 2 , and CK 3. Each isoenzyme is dimeric enzyme composed
of subunits M (muscle) or B (brain). The isoenzyme CK 1 contains subunit BB and
occurs primarily in the brain. CK 2 possess subunit MB and are found in the heart.
Skeletal muscles primarily contain the MM isoform (CK 3 ). Healthy individuals
typically contain the MM isoform and a small amount of the MB isoform in their
serum. The enzyme is not found in the liver, kidney, and blood cells. Various
conditions including skeletal muscle injury and myocardial damage release
CK-MB into the bloodstream. In myocardial infarction, levels of both CK-total
and CK-MB increase significantly, but CK-MB is considered a specific cardiac
marker.
33.2 Sample Requirement...............................
Serum or plasma (heparinized/EDTA) is used. Protect from light. Loss of activity
occurs within 7 days at 4C or within 24 h at 25C.
33.3 Principle........................................
Creatine kinase enzyme hydrolyzes creatine phosphate to liberate creatine and ATP
at pH 7.4. Enzyme hexokinase converts glucose to glucose-6-phosphate in presence
of ATP. Glucose-6-phosphate is converted to 6-phosphogluconolactone. The change
in absorbance is monitored at 30 s intervals for 3 min at 340 nm. The enzyme in
serum is relatively unstable and loses its activity due to sulfhydryl group oxidation at
the active site of the enzyme. The enzyme activity is partially restored by incubating
the enzyme reaction with sulfhydryl containing compounds such as
#Springer Nature Singapore Pte Ltd. 2018
V. Kumar, K. D. Gill,Basic Concepts in Clinical Biochemistry: A Practical Guide,
https://doi.org/10.1007/978-981-10-8186-6_33
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