Creatine Kinase

Question 1

What is creatine kinase used for?

Answer 1

To convert creatine phosphate into Creatine and ATP

Question 2

Where in the body is creatine kinase found in particularly high concentrations?

Answer 2

in the brain and muscle cells

Question 3

When is creatine kinase released into the circulation?

Answer 3

Following death / damage of brain and muscle cells

Question 4

How many isoforms are there of creatine kinase?

Answer 4

Three isoforms - can be identified through gel electrophoresis

Question 5

What are the three isoforms of creatine kinase?

Answer 5

MM, MB and BB

Question 6

What is the only place in which the MB isoform is found?

Answer 6

Cardiac muscle (myocardium)

Question 7

Which isoform moves closest to the negative electrode?

Answer 7

MM isoform

Question 8

What is myocardial infarct?

Answer 8

death of heart muscle cells

Question 9

What might cause a lack of oxygen resulting in a myocardial infarct?

Answer 9

Blockage of the cardiac arteries. This process is termed atherosclerosis and you might like to ponder on what kind of things might be risk factors for its early development.

Question 10

Why do cells need oxygen, how do they use it and why do cells die without it?

Answer 10

ATP is generated Via glycolysis, the Krebs Cycle and eventually oxidative phosphorylation.

The end point of the process requires atmospheric oxygen, hence if there is less oxygen supplied to a cell there is less ATP, pumps do not function, ion balance is lost and cells die.

Question 11

Why can the levels of proteins inside the blood be used to indirectly indicate cell death?

Answer 11

Cellular contents are released from cells when they are dying eg proteins which shuld be held against concentration gradients appear in the serum - Therefore the levels of many proteins including creatine kinase (many others as well such as lactate dehydrogenase) in serum can be used as indirect indicators of cell death.

Question 12

Describe the absorption spectrum for NADH and NAD+?

Answer 12

They are distinct

Question 13

What technique is used to detect CK activity in the serum?

Answer 13

coupled assay

Question 14

How then can increased CK be related specifically to the death of cardiac muscle rather than skeletal muscle and brain tissue?

Answer 14

The only tissue where both genes are expressed is cardiac muscle cells. They therefore make all three dimers including the hybrid MB form.
Thus, death of cardiac muscle fibres can be determined if the MB isoform of CK can be detected in the serum.

Question 15

Which form of creatine kinase is only expressed in the brain?

Answer 15

BB isoform as the brain only expresses the B gene

Question 16

Which isoform of creatine kinase is only found in skeletal muscle?

Answer 16

MM form is the only one made in skeletal muscle cells

Question 17

In what instance would measuring MM levels be useful?

Answer 17

to determine the extent of skeletal muscle damage in conditions like muscular dystrophy

Question 18

What is the level of MB isoform in the serum directly proportional to?

Answer 18

to the amount of cell death in the heart

Question 19

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

Answer 19

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

Question 20

In general how might you experimentally discern between different protein isoforms, what methods can be used?

Answer 20

Electrophoresis or column chromatography - but are slow and require expert technical operation. Neither are ideal in a Casualty Department.

Question 21

How many days after an heart attack is CK concentration highest?

Answer 21

24-48 hours after

Question 22

What are the four markers for myocardial damage?

Answer 22

Creatine Kinase

SGOT - Serum glutamate oxaloacetate transaminase

LDH - lactate dehydrogenase

cardiac troponin

Question 23

Why is cardiac troponin useful are a marker for myocardial damage?

Answer 23

Cardiac troponin I and troponin T are tissue specific and are not present in any other muscle. Their presence in the serum represents a specific marker for cardiac infarction (typically appearing in the serum after 48h of infarction and persisting for approximately 5 days).

Question 24

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

Answer 24

A semi-permeable membrane separates the inside from the outside of a cell, actively excluding some things e.g. Na+ions.

​This needs a protein pump in the membrane (ATPases)

They use energy in the form of adenosine triphosphate (ATP) to pump ions.

When no oxygen, no oxidative phosporylation, leading to no ATP, pumps stop working, homeostatic balance is lost, so things leak out the cells

Question 25

Why might the three isoenzymes be separated by electrophoresis?

Answer 25

CK is a protein made from 2 monomers = it is a dimer

The two monomers have approximately the same molecular but differ in their pI (isoelectric point).
This means that they can be separated by charge)