Creatine Kinase Flashcards
What does creatine kinase do
Creatine Kinase is responsible for catalysing the conversion of:
CREATINE PHOSPHATE ——> CREATINE
One molecule of ATP is generated in this reaction
What is the difference between necrosis and apoptosis
Necrosis = Death of many cells in an organ or tissue due to external physical damage (e.g. disease, injury or failure of blood supply). Apoptosis = Programmed cell death - a normal and controlled part of the organisms development.
In what tissues is CK present in high levels?
Muscle and the brain use a huge amount of ATP so needs high levels of creatine kinase.
CK is made of 2 subunits or monomers that are coded for by 2 different genes. Muscle only express the M gene so only makes CK of the MM form; the brain only expresses the B gene; the heart muscle cells are the only cells that express both genes and hence make dimers of the BM form.
There are different types of CK:
Muscle = MM
Brain = BB
Myocardium = BM
When and why is CK found in the blood?
Damage to the cell membrane allows leakage of CK into the blood stream.
What causes the plasma membrane of myocardial cells to become leaky?
Active transport membrane proteins (pumps) stop working because they require ATP to function. High concentrations of everything inside the cells leaks out.
How is CK activity detected
Creatine and Creatine Phosphate is not easily detectable so COUPLED ASSAYS are used.
Coupled Assay = Use 2 or more reactions to find something detectable. (i.e. the product of the first reaction becomes a substrate of the next and it goes on until an easily detectable product is formed.)
In the case of Creatine Kinase:
1. Creatine Phosphate + ADP ——————-> Creatine + ATP (Enzyme = Creatine Kinase)
2. ATP + D-glucose ———————-> ADP + Glucose-6-Phosphate (Enzyme = Hexokinase)
3. Glucose-6-Phosphate + NADP+ —————> 6-PG + NADPH + H+ (Enzyme = G6P dehydrogenase)
NADPH IS DETECTABLE! It absorbs UV light.
How can the isoenzymes be separated by electrophoresis
They have very similar molecular weights so they must be separated based on their charges. They each have different charges.
A quicker way of doing it is isoelectric focussing. You place the isoenzymes in the gel with a positive charge on one side and a negative charge on the other side; the isoenzyme will move to where it has a net charge of zero hence its ISOELECTRIC POINT (pI).
How might one establish a diagnosis of myocardial damage?
Elevated levels of MB creatine kinase in the serum.
Does an increase in serum CK activity relate to the size of myocardial damage?
Yes - levels of CK BM isoform in the serum are directly proportional to the amount of cell death in the heart. Each myocyte has a set amount of CK so when more cells are damaged, there is more CK.
What is the time course of serum CK after a myocardial infarction?
30 mins to 2.5 days
What other markers can be used for diagnosis of myocardial damage?
Lactate Dehydrogenase (LDH) - leaks out when cells are damaged. It is not particularly specific and only peaks after 6 days.
Troponin - there is a specific myocardium version - look for elevated levels of Troponin I and Troponin T, which are specific to cardiac muscle (appears after 48 hours and lasts 5 days).
Serum Glutamate Oxaloacetate Transaminase (SGOT) - starts being released from cells. Peaks as CK goes down.
Use antibodies which attach to the protein
