Tutorial 2 - Creatine Kinase and Myocardial Infarction

Question 1

What reaction does creatine kinase catalyse the conversion of?

Answer 1

Creatine phosphate ——–> Creatine

Question 2

Which 2 tissues have high levels of CK?

Answer 2

Muscle and brain and heart

Due to huge ATP requirements

(though CK is present in all cells at very low levels)

Question 3

How many different genes code for CK?

Answer 3

2.

2 subunits make a dimer

Question 4

What are the 3 types of CK?

Answer 4

1. Muscle = MM
2. Brain = BB
3. Myocardium = BM

Question 5

When and why is CK found in the blood?

Answer 5

When damage occurs to the cell membrane, CK leakage occurs into the bloodstream

Question 6

What may cause plasma cells of myocardial cells to become leaky?

Answer 6

1. Active transport membrane proteins stop working - they require ATP to function.
2. High concs of everything inside cell leaks out.

Question 7

How can CK activity be determined?

Answer 7

-1. C / CP are not easily detectable so coupled assays are used.

COUPLED ASSAY = using 2/more reactions to find something detectable.

1. Creatine phosphate + ADP ——-> Creatine + ATP (creatine kinase)
2. ATP + D-glucose ——> G6P + ADP (hexokinase)
3. G6P + NADP+ ——-> 6PG + NADPH + H+ (G6P dehydrogenase)

NADPH is detectable as it absorbs UV light

Question 8

How can the 3 CK isoenzymes be separated?

Answer 8

Using electrophoresis. They have similar molecular weights but all have different charges.

Question 9

What is a quicker way of separating the 3 CK isoenzymes?

Answer 9

Isoelectric focussing.

Place the isoenzymes in a gel with a positive charge on one end and a negative charge on the other end.

The isoenzyme will move to where it has a net charge of 0 (its ISOELECTRIC POINT).

Question 10

How can myocardial damage be established?

Answer 10

Elevated MB creatine kinase levels in serum.

Question 11

Is serum CK proportional to size of myocardial damage?

Answer 11

YES.

Each myocyte has a set amount of CK.

Question 12

Time course of serum CK after MI?

Answer 12

30 mins to 2.5 days.

peaks after 24 hrs

Question 13

What other markers can be used for cardiac damage?

Answer 13

1. LDH - not particularly specific and only peaks after 6 days
2. Troponin - look for elevated levels of Troponin 1 and Troponin T (specific to cardiac muscle). 48 hrs to 5 days
3. Serum Glutamate Oxaloacetate Transaminase (SGOT). Starts to be released from cells. Peaks as CK decreases.