Creatine Kinase

Question 1

How many dimeric isoenzymes of creatine kinase are found in humans?

Answer 1

Three isoezymes:
MM - skeletal muscle
BB - brain
MB - myocardium (15% of all CK)

Question 2

In what tissues is CK present at high levels?

Answer 2

Muscle and brain cells

Question 3

When and why is CK found in the blood?

Answer 3

Following the damage or death of cells CK is released into the circulation

Question 4

What is myocardial infarct (MI)?

Answer 4

Death of heart muscle cells

Question 5

Why do cells die?

Answer 5

Lack of oxygen

Question 6

Why would there be a lack of oxygen for myocardium?

Answer 6

Blockage of cardiac arteries (atherosclerosis)

Question 7

What causes the plasma membrane of myocardial cells to become leaky?

Answer 7

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

Question 8

How might you determine CK activity?

Answer 8

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+

Question 9

How can increased CK be related specifically to the death of myocardium rather than skeletal muscle or brain tissue?

Answer 9

Each isoform (M or B) has a specific pI (isoelectric point) which can help differentiate MB due to electric charge in electrophoresis

Question 10

Is a simple measure of CK activity in serum a sufficiently good diagnostic test for myocardial infarct?

Answer 10

No, because the activity could be from any of three tissues. Assay of the BM form is essential.

Question 11

Why is electrophoresis not used for CK identification?

Answer 11

Too slow

Question 12

Does an increase in serum CK activity relate to the size of myocardial damage?

Answer 12

Yes, as each myocyte is considered to have an equal volume

Question 13

Can we discriminate CK Type MB following an immunological approach?

Answer 13

Yes, by artifical manufacture of antibodies against desired proteins

Question 14

Identify the markers tested for MI on the figure (CK, SGOT, LDH)

Answer 14

CK - creatine kinase
SGOT - serum glutamate oxaloacetate transaminase (aka AT - aspartate transaminase)
LDH - lactate dehydrogenase

Question 15

What marker can be used for MI diagnosis other than CK, LDH, SGOT?

Answer 15

Cardiac troponin I and T

Question 16

How long after MI does cardiac troponin appear in serum?

Answer 16

typically appearing in the serum 48h after infarction and persisting for approximately 5 days