Isoenzymes

ISOENZYME

1. DIAGNOSTIC IMPORTANCE OF
ENZYMES
•FUNCTIONAL
ENZYMES
•Present in plasma
•Synthesised in liver
•Eg:
•Lipoprotein lipase
•Proenzymes of
clotting factors
•Digestive enzymes
•NON FUNCTIONAL
ENZYMES
•Absent in plasma
•Present in tissues in
higher concentrations
•Their presence in
plasma indicates
tissue damage
•eg: amylase
•ALP,SGOT,SGPT

2. ISOENZYMES
•Multiple form of enzymes catalysing same reaction
How it is formed?
1. May be products of different genes
Eg: salivary amylase &pancreactic amylase
2. Due to different subunits
Eg: LDH
3. Same locus of gene have different alleles
Eg: GDH
4.Due to the difference in the addition of carbohydrate
Eg: sialic content in ALP.

3. IDENTIFICATION OF
ISOENZYMES
•Gel electrophoresis
•Heat stability
•Inhibitors
•Km value
•Tissue localisation
They are differ in
•Physical properties
•Chemical properties
•Structure
•Km and vmax value
•Electrophorectic pattern

4. LACTATE DEHYDROGENASE
•Tetramer with foursubunits
•Subunits may be either H or M polypeptide chains
•Due to different combinations of H &M ,
5 isoforms are there.
ISOFORM SUBUNITS LOCATION
•LDH1 H4 Heart
•LDH2 H3M1 RBC
•LDH3 H2M2 Brain
•LDH4 H1M3 Liver
•LDH5 M4 Muscle
FUNCTION:
•CONVERTS LACTATE TO PYRUVATE.

5. CREATINE PHOSPHOKINASE
•Dimer
•Contains M and B subunits
•Has 3 isoforms.
ISOFORMSUBUNITSLOCATION
•CPK1 MM Muscle
•CPK2 MB Heart
•CPK3 BB Brain
FUNCTION:
CONVERTS CREATINE PHOSPHATE TO
CREATINE

6. Alkaline phosphotase
•Has 6 isoenzymes
•Monomer
•Isoenzymes are due to difference in carbohydrate
content.
1. alpha1 ALP - epithelial cells of
biliary canaliculi
2.alpha2 ht labile - hepatic cells
3.alpha2 ht stable - placenta
4.Pre beta Alp - bone
5.gammaALP - intestinal cells
6.Leukocyte ALP -

7. ENZYME PATTERN IN DISEASES
• MYOCARIDAL INFARCTION:
1. creatine kinase:
Normal value: Upto 100 u/l
First enzyme elevates within 3-6 hrs of MI
Highly useful index for early diagnosis of MI
MB isoform is elevated in MI
Goes upto 300 u/l within 24 hrs
Returns to normal within 2 to 3 days
OTHER CAUSES FOR ELEVATION:
Muscular dystrophies
Fractures
Crush injuries

8. 2. Lactate Dehydrogenase:
Normal value:100 – 200 u/l
Starts increasing form the second day
Goes upto 600 u/l on the 3 or 4 day
Takes 9 – 11 days to return to normal
Helps to diagnose late MI
Hemolysis of the sample gives false positive results.
Other causes:
Hemolytic anemia
Muscular dystrophy

9. 3. Aspartate transaminase (SGOT):
Normal value: upto 40 u/l
Raises after CPK
Reaches a peak within 2 days
Takes 4 – 5 days to return normal level
Moderately elevated in liver disease.

10. Cardiac troponin
•Connective tissue protein
•Contains 3 components
»1. troponin C
»2.troponin I
»3.troponin T
In MI
•Troponin I is released within 4 hrs
•Reaches peak within 1 day
•Remains elevated for 3-5 days
•75% sensitive index for MI
•Not increased in muscle injury
•Assayed by ELISA or RIA
* Troponin T is released within 6 hrs
* Reaches peak value at 72 hrs
* Remains elevated fro 7- 10 days
* 100 % sensitive index for MI

11. MYOGLOBIN
•Protein present in the muscle
•Very early protein released during MI
•Released in all tissue injury
•Non specific marker for MI

12. CARDIAC MARKERS
•TROPONIN T
•TROPONIN I
•CPK – MB
•LDH
•AST (SGOT)

13. ENZYMES IN LIVER DISEASE
1. Alanine transaminase( SGPT):
•Normal value: upto 40 u/l
•High values are seen in
»Acute hepatitis
•Moderate values are seen in
»Cirrhosis
»Malignancy of liver

14. 2. Aspartate transaminase (SGOT):
•Moderately increased in primary
hepatoma
•Both AST and ALT are in increased in
liver disease
• But ALT >>>> AST.

15. 3.Alkaline phosphotase (ALP):
Normal value: 40 – 120 u/l
Increased level in seen in children due to increased osteoblastic activity.
Mild increased level in seen in pregancy.
Moderately increased in
* infective hepatitis
* alcoholic hepatitis
* heptocellular carcinoma
Very high levels are seen in
* obstructive jaundice
* bone disease

16. 4. 5 ‘ Nucleotidase:
Normal value: 2 – 10 u/l
Moderately increased in hepatitis
Highly elevated in biliary obstruction

17. 5. Gamma glutamyl transferase(GGT):
Normal value: 2 -15 u/l
•Highly increased in alcoholism.
•Very sensitive marker for alcoholic abuse.

18. MARKER ENZYMES FOR LIVER
•ALT (SGPT)
•AST (SGOT)
•ALP
•5’ NUCLEOTIDASE
•GGT

19. ACUTE PANCREATITIS
•Salivary amylase