Creatine Kinase / Assay

From WikiLectures

The determination of creatine kinase activity is based on three consecutive enzyme reactions.

In the first creatine kinase catalyzed reaction, creatinine and ATP are formed. The formed ATP phosphorylates D-glucose to D-glucose-6-phospahte via hexokinase. In the last indicator reaction catalyzed by glucose-6-phosphate dehydrogenase, D-glucose-6-phosphate is oxidized to 6-phosphogluconate while reducing NADP+ to NADPH. In the UV region, we measure the increase in NADPH production, which is proportional to creatine kinase activity.

The catalytic activity of the CK-MB isoenzyme can be determined by a similar technique, but the reaction mixture must contain an additional antibody against the M subunit. Each subunit of creatine kinase performs a separate catalytic activity. Hence, in this technique, the activity of the isoenzyme CK-MM is completely inhibited, but the activity of CK-MB is halved. After the addition of the antibodies against M subunit, the initial catalyst concentration of CK-MB is simply calculated as twice the CK activity. When serum isoenzyme CK-BB is elevated (due to a breach in the blood brain barrier, most commonly caused by a transient ischemic attack), levels of released CK-MB determined by this technique are falsely high (often higher than the total CK activity).

Kategorie:Biochemie Kategorie:Klinická biochemie Kategorie:Kardiologie