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ENZYMES

BIOCHEMISTRY

mprasadnaidu
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ENZYMES

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  1. M.Prasad Naidu MSc Medical Biochemistry, Ph.D,. ENZYMES

  2. Classification of enzymes Based on the type of reaction enzymes can be classified into SIX MAJOR TYPES • Oxidoreductases- lactate dehydrogenase • Transferases- glucokinase • Hydrolases- chymotrypsin, G6Pase • Lyases- fumarase • Isomerases- phosphoglucoisomerase • Ligases- AcylCoAsynthetase

  3. OXIDOREDUCTASE Transfer of electrons (Hydride ions or H atoms) There are several subclasses 1) Dehydrogenases 2) Oxidases 3) Oxygenases

  4. Dehydrogenases aldehyde alcohol Oxidation of Ethanol by Alcohol Dehydrogenase Remove electrons and/or hydrogen atoms

  5. Oxygenases Catalyze incorporation of oxygen into a substrate Hydroxylation of Progesterone by a Monooxygenase

  6. TRANSFERASES Transfer functional groups in group transfer reactions Types of transferases 1) Amino transferases 2) Kinases 3) Glycosyl transferases

  7. Amino Transferases (or Transaminase) Transfer an amino group from one amino acid to a new keto acid

  8. Kinases Catalyze transfer of the phosphoryl group

  9. Glycosyl Transferases Transfer an activated glycosyl residue to a glycogen primer. This is a key enzyme in glycogen synthesis

  10. HYDROLASES Hydrolysis reactions The generalized reaction involves hydrolytic cleavage of C-O, C-N, O-P, and C-S bonds

  11. Peptidase Cleavage of a peptide bond by peptidases

  12. LYASES Addition or removal of elements of water, ammonia, or carbon dioxide

  13. Decarboxylases • Removal of an element of CO2 from a- and b-keto acids or amino acids

  14. Pyruvate Decarboxylase • The substrates bicarbonate and pyruvate are ligated to form a four-carbon (C4) oxaloacetate

  15. Dehydratases • Fumarase reversibly converts fumarate to malate. It removes H2O in a dehydration reaction converting malate to fumarate

  16. Isomerases Transfer of groups within molecules to yield isomeric form

  17. Epimerases • Isomerases that catalyze inversion at asymmetric carbon atoms

  18. LIGASES Involved in synthetic reactions where two molecules are joined at the expense of a high-energy phosphate bond of ATP

  19. 6.Ligases Biotin Acetyl CoA + CO2 MalonylCoA ATP ADP + Pi Enzyme is Acetyl CoAcarboxylase or Acetyl CoA-CO2ligase (systematic) code number EC.6.4.1.2ese enzymes link two substrates together, usually.

  20. Significance of Km • km indicates the affinity of enzyme to the substrate • Smaller the km larger the affinity • Larger the km smaller the affinity

  21. Substrate conc affects reaction velocity (rate) • As substrate concentration is increased, Initial velocityvi, increases until it reaches maximumVmax. • further increase in substrate concentration does not increase velocity the enzyme is said to be saturated. • Note that the shape of the graphic curve relating to catalytic activity and substrate concentration is hyperbolic

  22. Michaelis – menten equation illustrates in mathematical terms the relationship between initial reaction velocity , vi, and substrate concentration. Km = Michaelis constant Vmax = maximal velocity Vi = initial velocity [s] = substrate concentration Vmax [s] Vi = Km + [s]

  23. Km value or Michaelis – menten constant is defined as substrate concentration(expressed in moles / liter) to produce half maximal velocity in an enzyme catalysed reaction at a particular enzyme concentration. • It indicates that 50% of enzyme molecules are bound with the substrate molecules. • It’s a characteristic of an enzyme or signature of an enzyme. • Lower the Km value Higher the affinity of the enzyme for substrate. • Higher the Km value, the affinity of the enzyme for the substrate is low.

  24. Hexokinase Glucose Glucose-6-Phosphate ATP ADP Glucokinase HK Km value 10-2 mmol / L GK Km value 20 mmol / L

  25. Enzyme Patterns (Enzyme profiles) in diseses 1.Hepatic diseases 1.Alanine amino transferase (ALT) Marked increase in parenchymal liver disease 2. Alkaline phsophatase (ALP) Marked increase in obstructive liver disease 3.Nucleotide phsophatase (NTP) Elevated in liver dysfunction with cholestasis 4. Gamma glutamyl transferase (GGT) Increase in obstructive and alcoholic liver disease

  26. II.Myocardial Infarction: 1.Cratine Kinase (CK – MB) First enzyme to rise following infarction, CK-MB isoenzyme is specific. 2.Aspartate amino transferase (AST) Rises after the rise in CK and returns to normal in 4-5 days 3.Lactate dehydrogenase (LDH) Last enzyme to rise. LDH-1 becomes more than 2 (Flipped pattern)

  27. Enzyme pattern in Myocardial infraction AST

  28. Normal pattern of LDH in serum

  29. Flipped pattern of LDH in MI

  30. III.Muscle disease 1.Creatine Kinase (CK-MM) Marked increase in muscle disease. CK-MM fraction is elevated 2. Aspartate amino transferase (AST) Shows an increase in different types of muscle diseas; not specific 3. Aldolase Earliest enzyme to rise. But not specific

  31. IV. Bone diseases 1.Alkanine phosphatase (ALP) Marked elevationin osteoblastic bone activity as in rickets. Heat labile bone isoenzyme is elevated. Also in Paget’s disease. V.Prostate cancer 1.Prostate specific antigen (PSA) Marker for prostate cancer. Mild increase in benign prostate enlargement. 2. Acid phosphatase (ACP) Marker for prostate cancer . Metastatic bone disease especially from a primary from prostate.

  32. THANK YOU

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