Creatine Kinase
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How many dimeric isoenzymes of creatine kinase are found in humans?
Three isoezymes: MM - skeletal muscle BB - brain MB - myocardium (15% of all CK)
In what tissues is CK present at high levels?
Muscle and brain cells
When and why is CK found in the blood?
Following the damage or death of cells CK is released into the circulation
What is myocardial infarct (MI)?
Death of heart muscle cells
Why do cells die?
Lack of oxygen
Why would there be a lack of oxygen for myocardium?
Blockage of cardiac arteries (atherosclerosis)
What causes the plasma membrane of myocardial cells to become leaky?
No ATP production due to lack of oxygen → No active transport → Molecules such as CK and lactate dehydrogenase can’t be kept against the gradient → leaking occurs
How might you determine CK activity?
CK activity in the serum can be detected by a coupled assay leading to the generation of detectable products - NADPH has an absorption spectra distinct from NADP+
How can increased CK be related specifically to the death of myocardium rather than skeletal muscle or brain tissue?
Each isoform (M or B) has a specific pI (isoelectric point) which can help differentiate MB due to electric charge in electrophoresis
Is a simple measure of CK activity in serum a sufficiently good diagnostic test for myocardial infarct?
No, because the activity could be from any of three tissues. Assay of the BM form is essential.
Why is electrophoresis not used for CK identification?
Too slow
Does an increase in serum CK activity relate to the size of myocardial damage?
Yes, as each myocyte is considered to have an equal volume
Can we discriminate CK Type MB following an immunological approach?
Yes, by artifical manufacture of antibodies against desired proteins
Identify the markers tested for MI on the figure (CK, SGOT, LDH)
CK - creatine kinase SGOT - serum glutamate oxaloacetate transaminase (aka AT - aspartate transaminase) LDH - lactate dehydrogenase
What marker can be used for MI diagnosis other than CK, LDH, SGOT?
Cardiac troponin I and T
How long after MI does cardiac troponin appear in serum?
typically appearing in the serum 48h after infarction and persisting for approximately 5 days