Creatine Kinase Flashcards
Where is Creatine Kinase found?
In all cells but in high concentration in muscle cells, brain cells, heart cells.
When these cells are damaged or go through cell death CK is released into circulation.
What is Creatine Kinase?
Enzyme for reversible reaction of Creatine phosphate to Creatine + ATP
What Three Dimeric isoenzymes of Creatine Kinase to the subunits M and B create?
MM ( muscle )
BB ( Brain )
MB ( 15 % of Myocardium )
How can we separate the three isoenzymes?
Electrophoresis on cellulose acetate strips.
MM moved furthest to negative electrode.
( can be used to see if any CK is in plasma )
What causes plasma membrane of myocardial cells to become leaky?
Blockage of cardiac arteries ( atherosclerosis ) causes lack of oxygen.
No O phosphorylation, No ATPase pump action. No ATP, no ion balance and hence cell necrosis
CK and others can go leak out of concentration gradient
How can you determine CK activity?
Coupled assay leading to generation of detectable products.
Can indirectly check absorption spectra of NAD+ and NADh, NADH will increase with CK:
creatine phosphate + ADP –> [ CK ENZYME ] Creatine+ATP
D-glucose+ATP –> [ hexokinase ] ADP + G6P
G6P + NADP –> [ G6P dehydrogenase ] 6-PG + NADPH + H+
Why can we use electrophoresis to separate three isoenzymes?
M and B isoforms are coded by their own genes.
They have the same molecular point but differ in Isoelectric point = can be separated by charge
How can Myocardial damage be diagnosed?
Only cardiac muscle cells have both genes expressed for M and B isoforms. And make all three dimers MM,BB and MB.
If BM isoform of CK can be detected = myocardial damage
Does an increase in serum CK activity relate to the size of myocardial damage?
Directly proportional to amount of cell death
How long does CK remain in the serum after infarction?
What other markers are there in serum?
Peaks in serum at one day and then levels decrease
SGOT ( Serum glutamate oxaloacetate transaminase ) if heart attack was over one day ago
LDH ( Lactate dehydrogenase ) a small peak on graph, not a good signal or a myocardial infarction as LDH can leak out of many cells
What other marker can we use to determine a myocardial infarction but it is not available on the NHS?
Troponin is the calcium switch in muscle. Cardiac troponin I and troponin T are tissue specific and are not present in any other muscle.
Cardiac Troponin I and T, appears in serum 48 hours after and up to 5 days
Structure of CK?
CK is a protein made from two subunits or monomers i.e. it is a dimer.
The two monomers are coded for by two different genes.
These generate two different monomer isoforms “B” and “M”. The two monomers have approximately the same molecular weigh (43 kDa) but differ in their pI (the pI for the B isoform is 6.77, while the pI for the M isoform is 5.34).
Monomers associate and bind to one another in the cytoplasm to produce active dimers (Figure 2).
Why is CK BM isoform in serum directly proportional to cell death in the heart??
This is because each myocyte can be considered to be approximately of equal volume (they have equal likelihood of dying independently of their size) so, as each cell dies it releases a “quantum” of CK into the extracellular fluid and thence into the serum.
Immunological approach to pick individual proteins?
artificial manufacture of antibodies against desired proteins.
