Lecture 8: Plasma Enzyme and Myocardial Infarction

Question 1

What is an enzyme and its purpose?

Answer 1

protein that catalyses one or more specific biochemical reactions.

Enzymes perform the critical task of lowering a reaction’sactivation energy

Question 2

What is the induced fit for an enzyme?

Answer 2

Lecture slide

Question 3

What causes a rise in enzyme levels in the body?

Answer 3

1. Necrosis or severe damage to cells
   2.Increased rate of cell turnover during active growth, tissue repair or in cancer.
   3.Increased concentrations of enzymes within cells, usually as a result of induction by disease or drugs.
   4.Obstruction-regurgitated into the blood if the normal route of the outflow is obstructed.

Question 4

3 variants of enzymes and description

Answer 4

Isoenzymes
proteins with similar enzymic activities which typically appear in different organs and subcellular organelles.

Alloenzymes
Genetically determined variants of an enzyme protein which only occur in different individuals of the same species.

Heteroenzymes
Proteins with a similar enzyme activity form different species.

Question 5

3 origins of enzymes

Answer 5

Plasma enzymes
actively excreted into the plasma where they exert their biological function

Secreted enzymes
released from the tissue of origin and a portion is found in the plasma.

Key pathway enzymes
enzymes that are part of key metabolic pathways

Question 6

Factors affecting enzyme activity

Answer 6

Analytical Factors
substrate concentration
Incubation time
Enzyme concentration
pH
Temperature effects

Physiological factors affecting enzyme activities.
Age
Sex
Physiological conditions

Question 7

Ischemic Heart disease:
What is it?
Caused by?

Answer 7

heart problems caused by narrowed heart (coronary) arteries that supply blood (oxygen) to the heart muscle.

is caused by an imbalance between the myocardial blood flow and the metabolic demand of the myocardium.

Question 8

Factors reducing coronary flow

Answer 8

Decreased Aortic diastolic pressure.
Increased ventricular pressure.
Coronary heart stenosis (Slow build-up of fatty plaque within the artery wall can cause the artery to narrow, reducing blood flow).
Aortic artery thrombosis (formation of blood clot).
Increased atrial pressure.

Question 9

Pathogenesis of heart attack?

Answer 9

1. Usual reason is that a blood clot (thrombosis) forms inside a coronary artery, or one of its branches. However, a clot may form if the artery has some atheroma on its inside lining.

2.Atheroma (fatty patches or ‘plaques’), which develop on the inside lining of arteries

3.A ‘crack’ in a patch of atheroma can trigger the clotting mechanism in the blood to form a blood clot

MY NOTES
Most common is thrombosis on a preexisting disrupted atherosclerotic plaque causing complete obstruction of the coronary arteries. In the following sequence of events
(1) The initial event is a sudden change in the structure of an atheromatous plaque, that is, disruption as intra plaque hemorrhage, ulceration, or rupture.
(2) Exposure of the thrombogenic subendothelial basement membrane and necrotic plaque contents resulting in thrombus formation.
(3) Frequently within minutes, the thrombus evolves to completely occlude the lumen of the coronary vessel.

Question 10

Cardiac Biomarkers:
What are they and where are they found?

Answer 10

CK, LDH, creatine Kinase MB, Troponins, myogloblin, homocysteine, CRP.
Found in the blood normally but are elevated during attack suggesting major damage to the heart muscle

Question 11

CK Test description and is it specific?

Answer 11

an enzyme found in the heart, brain, skeletal muscle, and other tissues.

Increased amounts of CK are released into the blood when there is muscle damage.

This test measures the amount of creatine kinase in the blood.

Non specific: A high CK, or a rise in levels in subsequent samples, generally indicates that there has been some recent muscle damage but will not indicate its location or cause.

Question 12

LDH Test levels after attack and is it specific?

Answer 12

Rise in 12-24 hours after attack, peaks 2-3 days and dissaptes in 5-14 days

Measurement of LDH isoenzymes is necessary for greater specificity for cardiac injury.

Question 13

Creatine Kinase-MB Test and is it specific?

Answer 13

is a form of an enzyme found primarily in heart muscle cells.

This test measures CK-MB in the blood. MB fraction is much more specific for cardiac muscle

is a very good marker for acute myocardial injury, because of its excellent specificity, and it rises in serum within 2 to 8 hours of onset of acute myocardial infarction and stays high for 36-48 hours.

Question 14

Troponin Test and is it specific?

Answer 14

Are a group of proteins found in skeletal and heart (cardiac) muscle fibers that regulate muscular contraction.

Troponin tests measure the level of cardiac-specific troponin in the blood to help detect heart injury.

Troponin I and T are structural components of cardiac muscle.

They are highly specific for myocardial injury, help to exclude elevations of CK with skeletal muscle trauma. will begin to increase following MI within 3 to 12 hours, about the same time frame as CK-MB. However, the rate of rise for early infarction may not be as dramatic as for CK-MB.

Question 15

Myoglobin Test and is it specific?

Answer 15

is a protein found in skeletal and cardiac muscle, which binds oxygen
rise in myoglobin can help to determine the size of an infarction.

not specific for cardiac muscle, and can be elevated with any form of injury to skeletal muscle.

Question 16

Homocysteine Test

Answer 16

a normal breakdown product of the essential amino acid, methionine, is believed to exert several toxic effects.

elevated homocysteine level is a risk factor for heart disease, independent of other known risk factors, such as elevated serum cholesterol and hypertension.

Question 17

CRP Test

Answer 17

When LDL accumulates in the intima, it activates the endothelium to express leukocyte adhesion molecules and chemokines that promote recruitment of monocytes and T cells. The result is higher levels of CRP in patients with atherosclerosis than in those without atherosclerosis.

C-reactive protein (CRP) is an acute phase reactant.
An atheroma, or atheromatous plaque (“plaque”), is an abnormal accumulation of material in the inner layer of the wall of an artery.

The material consists of mostly macrophage cells, or debris, containing lipids, calcium and a variable amount of fibrous connective tissue.

Atheromatous plaques in diseased arteries typically contain inflammatory cells.

As a potential marker of an “unstable” atheromatous plaque and underlying atherosclerosis.

Question 18

Lipoprotein test

Answer 18

Lipoprotein Lp(a) excess has been identified as a powerful predictor of premature atherosclerotic vascular disease.

Levels modulate the risk of coronary heart disease in patients with hypercholesterolemia, and lipoprotein Lp(a) excess is commonly detected in men and women with premature coronary atherosclerosis.

Question 19

The relationship between an enzyme and a reactant molecule can best be described as ________________

Answer 19

temporary association.

Question 20

why are enzyme levels constant inside cells

Answer 20

In the cell the concentration of many enzymes remains relatively constant due to equilibrium between synthesis and degradation.

Question 21

what does disease do (cellular level) that causes a rise in enzyme level

Answer 21

In many diseases the release of enzymes is enhanced by increased permeability of the cell membranes, by breakdown of the cell structure or occasionally by increased synthesis (enzyme induction).