Enzymes II

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ENZYMES-II Mechanism of action:

ENZYMES-II Mechanism of action Dr. Hariharan MD, Assistant Professor, Dept of Biochemistry, Karpagam Faculty of medical Sciences and Research, Coimbatore. Dr. Hariharan . V, free download available in Internet (author stream)

Introduction :

Introduction Enzyme catalyse the conversion of one or more compounds (Substrates) into one or more different compounds(Products) Enzymes are effective- They enhance the rate of reaction of a minimum of 10 6 times. They are selective- they are specific for both the type of reaction, specific for a particular substrate and selective to a particular isomer of the substrate. Dr. Hariharan. V, free download available in Internet

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Prosthetic groups, cofactors, co enzymes:

Many enzymes contain small non protein molecules that participate in enzyme action. They are prosthetic groups, co factors or co enzymes. Prosthetic Groups: They incorporate stable and tight to the enzymes by covalent or non covalent interactions. Eg . Flavin adeno dinucleotide (FAD) Flavin Mono Nucleotide(FMN) Thiamine Pyrophosphate(TPP) Biotin Metal ions- Co, Cu, Mg, Mn and Zn. They complex tightly with enzymes forming Metallo enzymes. They participate in redox reactions- eg . Heme Facilitate substrate binding Formation of covalent bond between reaction intermediates Prosthetic groups, cofactors, co enzymes Dr. Hariharan. V, free download available in Internet

Cofactors :

Cofactors They associate in a transient, dissociable manner to enzyme or the substrate They should be present in the medium surrounding the enzyme for catalysis to occur Eg. Metals They are called metal activated enzymes Dr. Hariharan. V, free download available in Internet

Co enzymes:

Co enzymes They act as a shuttle. They transport many substrates from the point of generation to the point of catalysis Eg . Co enzyme A- attaches acyl group Folate - methyl groups NAD, NADP- H + Properties of prosthetic groups, co factors and enzymes: Most of them are derived from B vitamins. Eg . FAD, FMN- Riboflavin NAD, NADP- Niacin TPP- Thiamine CoA - Pantothenic acid Folate - Folic acid Biotin Dr. Hariharan. V, free download available in Internet

Active site:

Active site Enzymes are specific to substrates. So enzyme should possess a site which will bind to specific group of a specific substrate and does only a specific reaction. That site where the substrate binding and catalysis occurs is called active site. Usually it is situated in a crevice or cleft of the enzyme molecule. The active sites recruits residues( aminoacids ) of the enzyme from various polypeptide chains. The aminoacids or groups that takes place in catalytic reaction are called catalytic residues or groups. Dr. Hariharan. V, free download available in Internet

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Substrates binds to the active site at a region complementary to a portion of substrate which wont undergo catalysis This binding causes the portion of substrate which should be catalysed to automatically bind to the functional groups of the aminoacids in the active site. The active site also binds to cofactors and co enzymes of the active site Dr. Hariharan. V, free download available in Internet

Mechanisms of catalysis:

Mechanisms of catalysis Catalysis by proximity: -For molecules to react they must come within bond forming distance of each other. -when substrates bind to the active site it creates an environment of high concentration of the substrates, which will cause increased collision and chemical reaction Dr. Hariharan. V, free download available in Internet

2. Acid Base catalysis:

2. Acid Base catalysis The functional groups in the aminoacids in the active site act as an acid or base and causes conformational change in substrates Eg. HIV protease Dr. Hariharan. V, free download available in Internet

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e - Dr. Hariharan . V, free download available in Internet R 1 -NH-C -R 2 O B-Aspartate-COO - HO H Base e - B-Aspartate-COO H OH - e - R 1 -NH-C -R 2 O - OH Tetrahydral transition state intermediate A-Aspartate-COO H acid A-Aspartate-COO - C -R 2 R 1 -NH- H + O OH HIV protease

3. Catalysis by strain:

3. Catalysis by strain Enzymes involved breaking bond of the substrate bind the substrates in a conformation that is unfavorable to the bond  results in strain to that bondweakens the bond breakage Dr. Hariharan. V, free download available in Internet

4. Covalent catalysis:

4. Covalent catalysis The enzyme forms an covalent bond with the substrate. It is common in group transferring enzymes. At the end of reaction, enzyme attains its native chemical structure. Eg. Chymotrypsin Dr. Hariharan. V, free download available in Internet

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O e - 102. -Asp- COO - - 57. His - 195. Ser R 1 -NH-C -R 2 O e - e - O - OC-- -H-N-N-- H-O R 1 -NH-C -R 2 O - O Ser 102. -Asp- COO - - 57. His - H O - OC-- -H-N-N-- H R 1 -NH 2 C -R 2 + O Ser 102. -Asp- COO - - 57. His e - e - HO H H + O H HO-C -R 2 O - O Ser 102. -Asp- COO - - 57. His - H HOOC -R 2 Chymotrypsin

Other mechanisms of action:

Other mechanisms of action Lock and key model Koshland’s induced fit model Dr. Hariharan. V, free download available in Internet

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Dr. Hariharan. V, free download available in Internet Thank you References: Harper’s Biochemistry Vasudevan

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