L9: Biomedical significance of enzymes

Question 1

What is the definition of isoenzymes?

Answer 1

Iso = the same

Different molecular forms of the enzyme, have the same
catalytic activity.

Question 2

What are the characters of isoenzymes?

Answer 2

Although they have the same catalytic activity, they are physically distinct & differ in:
1) Electrophoretic mobility (migration in an electric field).
2) Liability to inhibitors.

Question 3

What are examples of isoenzymes?

Answer 3

 Lactate dehydrogenase (LDH)
 Creatine kinase (CK)
 Acid phosphatase
 Alkaline phosphatase

Question 4

LDH

Answer 4

❖ LDH enzyme is a tetramer formed of (4) protein subunits, each subunit is called protomer.
❖ The subunits of LDH are of 2 types, H (heart) and M (muscle).

Question 5

LDH types

Answer 5

LDH 1 HHHH Myocardial infraction

LDH 2 HHHM Myocardial infraction

LDH 3 HHMM Leukemia

LDH 4 HMMM Viral hepatitis

LDH 5 MMMM Viral hepatitis

Question 6

Creatine kinase (CK)

Answer 6

❖ CK enzyme is a dimmer formed of 2 protein subunits.
❖ The subunits of CK are of 2 types, B (brain) and M (muscle

Question 7

CK types

Answer 7

CK BB BB Brain tumors
CK MB BM Heart diseases
CK MM MM Skeletal muscle diseases

Question 8

What are the sources of isoenzymes?

Answer 8

1- True genetic variants (True isoenzyme)
 may be produced by more than one gene; each gene produces one subunit

2- Multiple forms (post-translational modification)
 Isoenzymes may be produced by the same gene, but the subunits undergo different post-translation modifications in different organs

Question 9

What is the medical importance of isoenzymes?

Answer 9

Isoenzymes are important in the diagnosis of diseases and indication of the diseased organ

Question 10

What are the types of plasma enzymes?

Answer 10

❖ Plasma contains many enzymes: Functional and non-functional plasma enzymes

Question 11

Functional plasma proteins Vs. non-functional plasma proteins

Answer 11

 Higher in comparison to tissue
 Have known functions
 Always present in plasma
 Liver
 They decrease in liver diseases

Ex:-
 Clotting factors e.g. Prothrombin
 Lipoprotein lipase
 Pseudocholinesterase

 Very low in comparison to tissue
 No known functions
 Absent from plasma
 Different organs e.g. liver, heart, skeletal muscles, and brain
 They increase in different organ diseases

Ex:-
 ALT, AST, Alkaline phosphatase
 Acid phosphatase
 Lipase

Question 12

What are the sources of non-functional plasma enzymes?

Answer 12

❖ Obstruction of the normal pathway.
❖ Increased permeability of cell membrane: as in tissue hypoxia.
❖ Cell damage with the release of its contents of enzymes into the blood.

Question 13

What is the medical importance of non-functional enzymes?

Answer 13

ALT: Liver disease
AST: Liver, heart disease
CK: Brain tumors, Myocardial infarction, SM disease
LDH: Myocardial infarction, Leukemia, Viral hepatitis
Alk. Phosphatase: Obstructive liver disease, bone disease
Acid phosphatase: Prostate cancer
Amylase, lipase: pancreatitis