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Classification of enzymes and properties of enzymes


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classification of enzymes into 6 major classes and then into minor sub-classes , properties

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Classification of enzymes and properties of enzymes

  1. 1. TRANSFERASES Transfer of functional groups from one molecule to another molecule. 5 subclasses  Transaminases  Kinases  Transmethylases  Transpeptidases  Transacylases
  2. 2. TRANSAMINASES Catalyze exchange of –NH2 group b/w amino acid & keto acid. COOH COOH COOH COOH │ │ │ │ H2NCH C=O AST C=O H2NCH │ + │ │ + │ CH2 CH2 CH2 CH2 │ │ │ │ CH2 COOH CH2 COOH │ │ COOH COOH G.A OAA αKG AA
  4. 4. PHOSPHOTRANSFERASES Catalyze transfer of phosphate group Glucose + ATP Glucose-6-P + ADP TRANSMETHYLASES Catalyze transfer of methyl group
  5. 5. TRANSPEPTIDASES Transfer of amino acid or peptides TRANSACYLASES Transfer of Acyl group  Acetyl CoA + Choline Acetylcholine+CoA
  6. 6. HYDROLASES Catalyze hydrolysis reactions PROTEIN HYDROLYZING ENZYMES EXOPEPTIDASES  POLYPEPTIDASES aminopolypeptidases carboxypolypeptidases  TRIPEPTIDASES  DIPEPTIDASES ENDOPEPTIDASES Trypsin, Pepsin,Chymotrypsin,Elastase
  7. 7. CARBOHYDRASES Hydrolysis of glycosidic bond. e.g. Amylase, Maltase, Sucrase, Lactase LIPID HYDROLYZING ENZYMES I. LIPASES act on TAG II. CHOLESTERYL ESTERASE hydrolyze C – esters III. PHOSPHOLIPASES act on PL
  8. 8. DEAMINASES adenase Adenine + H2O Hypoxanthine + NH3 guanase Guanine + H2O Xanthine + NH3 DEAMIDASES Catalyze hydrolysis of amides. Urea + H2O CO2 +2NH3 Arginine + H2O Ornithine+ Urea
  9. 9. OTHER ESTER HYDROLYZING ENZYMES PHOSPHATASES  PHOSPHOMONOESTERASES e.g. Acid phosphatase , alkaline phosphatase G-6-P + H2O Glucose + Phosphoric acid  PHOSPHODIESTERASES Splits off one phosphate group of diesters.
  10. 10.  PHOSPHORYLASES Add inorganic phosphate (Pi) to split bond. glycogen phosphorylase Glycogen + H3PO4 Glucose I-P  PYROPHOSPHATASES Hydrolyze pyrophosphates(PPi) PPi +H2O 2Pi  NUCLEASES Decompose nucleic acid.( polynucleotides to mononucleotides) .
  11. 11.  NUCLEOTIDASES Hydrolyze mononucleotides to nucleosides & H3PO4.  NUCLEOSIDASES Nucleoside + H3PO4 free nitrogen base + sugar phosphate MISCELLANEOUS  CHOLINESTERASE acetylcholine to acetic acid & Choline.  SULFATASE Catalyze hydrolysis of sulfate esters.
  12. 12. LYASES Catalyze addition of NH3, H2O, CO2 to double bond or their removal from double bond. COOH COOH │ fumarase │ CH + H2O HOCH ║ │ HC CH2 │ │ COOH COOH Fumaric acid Malic acid
  13. 13. ISOMERASES Catalyze structural change within a single molecule by transfer of group within it resulting in formation of an isomeric form of the substrate. phosphohexose isomerase Glucose-6-P Fructose 6-P e.g. racemases,epimerases,cis-trans isomerases.
  14. 14. LIGASES Catalyze condensation reactions joining two molecules by forming C-O, C-S, C-N, C-C bonds along with energy releasing hydrolysis or cleavage of high energy phosphates. CH3 Acetyl CoA COOH │ carboxylase │ C=O + CO2 +ATP CH2 + ADP + Pi │ │ S-CoA C=O │ S-CoA Acetyl CoA Malonyl CoA
  16. 16. 1. SPECIFICITY Specific in their action though to a variable extent.  ABSOLUTE SPECIFICITY CA CO2 + H2O H2CO3  RELATIVE SPECIFICITY Pancreatic esterase; hydrolyze both aliphatic esters & Cholesteryl esters.
  17. 17.  BOND SPECIFICITY TRYPSIN; hydrolyze residue of only lysine & arginine. LIPASES; hydrolyze ester bond.  GROUP SPECIFICITY one enzyme catalyze same reaction on a group of structurally similar compounds. HEXOKINASE; catalyze Phosphorylation of glucose,fructose,mannose.  STEREOSPECIFICITY Enzymes distinguish b/w D-& L-sugars as well as D-& L- amino acids.
  18. 18. 2. PROTEIN NATURE Enzymes are protein in nature Except few RNAs 3. DIRECTION OF ENZYME REACTION BIDIRECTIONAL A + B C + D UNIDIRECTIONAL A + B C + D
  19. 19. 4.PROENZYMES  Inactive form of enzymes.  Active site of enzyme is masked by a small region of peptide chain that is removed by hydrolysis of specific bond.  Prevent autolysis of cellular structural proteins. e.g. Pepsinogen ; pepsin by gastric HCL Trypsinogen ; trypsin 5.ENZYME LOCATION Cytosol ; F.A synthesis Mitochondria ; F.A oxidation
  20. 20. 6.ENZYMES CATALYZING RATE - LIMITING REACTIONS Enzyme catalytic efficiency determines efficiency of an entire metabolic reaction. HMG-CoA reductase cholesterol synthesis ↓ statin drugs inhibit it. 7.ENZYME INDUCTION Enzymes previously absent or present only in traces in certain microorganisms can be induced by substances called INDUCERS, which in many cases are actual substrates. e.g. Induction of penicillanase by penicillin in bacteria
  21. 21.  Phenobarbitone induces synthesis of many hepatic microsomal enzymes including bilirubin glucuronyl transferase.  Barbiturates ↑ δ ALA synthetase & precipitates acute intermittent porphyria. 8.ENZYME REPRESSION  INSULIN induces enzymes of glycolysis  GLUCAGON represses them  E.COLI make tryptophan synthetase when medium doesn't contain tryptophan.
  22. 22. 9.ISOZYMES Physically distinct version of a given enzyme, each of which catalyze the same reaction. LDH , 5 isozymes LDH I HHHH (heart) LDH 2 HHHM LDH3 HHMM LDH4 HMMM LDH5 MMMM (muscles) CK , 3 isozymes CK 1 BB (brain) CK 2 BM (heart) CK 3 MM (sk. Muscles)
  23. 23. DIAGNOSIS OF MI  Regulatory proteins involved in myocardial contractility. Troponin I & Troponin T  Enzymes of diagnostic importance CK AST LDH
  24. 24. DIAGNOSIS OF MI ENZYME TIME OF ONSET PEAK LEVEL DURATION OF RISE TROPONIN I 4-6 hr 8-24 hr 3-10days CK-MB 4-8hr 12-24hr 48-72hr AST 6-8hr 24-48hr 3-5days LDH 12-24hr 48-72hr 7-12days