Isoenzyme.pptx

Isoenzymes (or isozymes) are a group of enzymes that catalyze the same reaction but have different enzyme forms and catalytic efficiencies. Isozymes are usually distinguished by their electrophoretic mobilities.

1. ISOENZYMES By Mr. Abhijit Bhoyar Department of Child Health Nursing

2. Specific Learning Objectives At the end of the lecture, student should be able to: Define isoenzymes Explain properties of isoenzyme

3. Introduction The multiple forms of an enzyme catalysing the same reaction are isoenzymes or isozymes . They, however, differ in their physical and chemical properties which include the structure, electrophoretic and immunological properties, K m and V max values, pH optimum, relative susceptibility to inhibitors and degree of denaturation.

4. Isoenzymes Definition Isoenzymes is a group of enzymes that catalyze the same reaction but have different enzyme forms and catalytic efficiencies.  

5. In biochemistry, isozymes are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. Isozymes usually have different kinetic parameters, or are regulated differently. They permit the fine-tuning of metabolism to meet the particular needs of a given tissue or developmental stage.

6. Types

7. Explanation for the existence of isoenzymes Many possible reasons are offered to explain the presence of isoenzymes in the living systems. 1. Isoenzyme s synthesized from different genes e.g. malate dehydrogenase of cytosol is different from that found in mitochondria. 2. Oligomeric enzymes consisting of more than one type of subunits e.g. lactate dehydrogenase and creatine phosphokinase.

8. Cont.. 3. An enzyme may be active as monomer or oligomer e.g. glutamate dehydrogenase. 4. In glycoprotein enzymes, differences in carbohydrate content may be responsible for isoenzymes e.g. alkaline phosphatase.

9. Isoenzymes of lactate dehydrogenase (LDH) LDH whose systematic name is L- lactateNAD + oxidoreductase (E.C. 1.1.1.27) catalyses the interconversion of lactate and pyruvate

10. Structure of LDH isoenzymes : LDH is an oligomeric ( tetrameric ) enzyme made up of four polypeptide subunits. Two types of subunits namely M (for muscle) and H (for heart) are produced by different genes. M–subunit is basic while H subunit is acidic. The isoenzymes contain either one or both the subunits giving LDH1 to LDH5 .

11. Significance of differential catalytic activity : LDH1 (H4) LDH1 (H4) is predominantly found in heart muscle and is inhibited by pyruvate – the substrate . Hence, pyruvate is not converted to lactate in cardiac muscle but is converted to acetyl CoA which enters citric acid cycle. LDH5 (M4 ) is mostly present in skeletal muscle and the inhibition of this enzyme by pyruvate is minimal,hence pyruvate is converted to lactate. Further,LDH5 has low Km (high affinity) while LDH1 has high Km (low affinity) for pyruvate.

12. The differential catalytic activities of LDH1 and LDH5 in heart and skeletal muscle, respectively, are well suited for the aerobic (presence of oxygen) and anaerobic (absence of oxygen) conditions , prevailing in these tissues.

13. Diagnostic importance of LDH : Isoenzymes of LDH have immense value in the diagnosis of heart and liver related disorders In healthy individuals, the activity of LDH2 is higher than that of LDH1 in serum. In the case of myocardial infarction, LDH1 is much greater than LDH2 and this happens within 12 to 24 hours after infarction. Increased activity of LDH

14. Isoenzymes of creatine phosphokinase Creatine kinase (CK) or creatine phosphokinase (CPK ) catalyses the inter-conversion of phosphocreatine (or creatine phosphate) to creat

15. Isoenzymes of alkaline phosphatase As many as six isoenzymes of alkaline phosphatase (ALP) have been identified. ALP is a monomer, the isoenzymes are due to the difference in the carbohydrate content ( sialic acid residues). The most important ALP isoenzymes are D1-ALP, D2-heat labile ALP , D2-heat stable ALP, pre-E ALP, J-ALP etc

16. Isoenzymes of alcohol dehydrogenase Alcohol dehydrogenase (ADH) has two heterodimer isoenzymes . Among the white Americans and Europeans, DE1 isoenzyme is predominant whereas in Japanese and Chinese (Orientals ) DE2 is mostly present. The isomer DE2 more rapidly converts alcohol to acetaldehyde.

17. Properties of isoenzymes Electrophoretic - E.g Isoenzymes of Lactate dehydrogenase have mobility different electrophoretic mobility Heat stability - E.g Alkaline phosphatase isoenzymes are either heat labile or stable Inhibitor - E.g An inhibitor can inhibit only one isoenzyme of an enzyme eg . Acid phosphatase

18. Cont.. 4. Cofactors Mitochondrial isocitrate dehydrogenase requires NAD+ , cytosolic form requires NADP+ 5. Tissue localization- Eg LDH 1 is present in heart, LDH 5 in muscle 6. Antibodies -For creatine kinase, each isoenzyme can be bound only by a specific antibody 3

19. Expsected Question Essay / Situational Question Describe isoenzymes with reference to definition and properties , chemical nature and factors affecting isoenzyme activity Short Question Explain characteristic of isoenzyme Describe Classification of isoenzyme Describe factors influencing isoenzyme activity

20. THANK YOU