Tutorial 2 - Creatine Kinase and Myocardial Infarction Flashcards
Creatine Kinase Background
enzyme that catalyses the conversion of creatine phosphate –> creatine, generating 1 mol. ATP.
Present in all cells in very low levels
In which tissues is CK present in high levels?
Muscle and Brain (use large amounts of ATP).
CK is made from 2 subunits coded by 2 different genes.
Muscles only express M gene (MM), brain only expresses B gene (BB).
Heart muscle cells are the only cells that express both genes and make dimers of BM form.
When and Why is it found in the blood?
Damage to the cell membrane allows leakage of CK into the bloodstream
What causes the plasma membrane of heart cells to become leaky?
active transport membrane proteins stop working, requiring ATP to function. high concentrations of everything in the cells leaks out.
How to determine CK activity?
Coupled Assays - as not easily detectable.
- Creatine Kinase + ADP –> Creatine + ATP (creatine kinase)
- ATP + D-glucose –> ADP + G6P (hexokinase)
- Glucose-6-Phosphate + NADP+ –> 6-PG + NADPH + H+
NADPH IS DETECTABLE = IT ABSORBS uv LIGHT
Why can the three isoenzymes be separated by electrophoresis?
They would have similar weights so would need to be separated by charge.
this could be done by ISOELECTRIC FOCUSSING - place them in gel with positive and negative side, they would move until they reach their isoelectric point (net charge = 0)
How do you establish a diagnosis of myocardial damage?
Does an increase in serum CK activity relate to the size of myocardial damage?
Elevated levels of MB creatine kinase in the serum
Yes, levels of CK BM isoform are directly proportional to the amount of cell death in the heart, each myocyte having a set amount of CK
Time course of serum CK after a myocardial infarction?
30 mins to 2.5 days
Other markers of myocardial damage?
Lactate Dehydrogenase - leaks out when cells are damaged - not specific, peaks after 6 days.
Troponin - look for T I and TT specific to the myocardial muscle ( 2-7 days)
Serum Glutamate Oxaloacetate Transaminase (SGOT) - starts immediately, peaks as CK decreases.
