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BCH461_Chapter6

BCH461_Chapter6 - Chapter 6 Enzymes 1 An introduction to...

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Chapter 6 Enzymes •1 An introduction to Enzymes •2 How enzymes work •3 Enzyme kinetics •4 Types of enzymatic reactions
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Enzymes are biological catalysts • Sugar + O 2 -> energy + CO 2 + H 2 O Catalysts are substances that increase the rate, or velocity, of a chemical reaction without itself being changed in the overall process. Enzymes are biological catalysts that are highly specialized proteins with extraordinary catalytic power high degree of specificity function in aqueous solutions under mild conditions of T and pH.
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Catalytic Power Enzymes can accelerate reactions as much as 10 17 over uncatalyzed rates! Urease is a good example: – Catalyzed rate: 3x10 4 s -1 – Uncatalyzed rate: 3x10 -10 s -1 – Ratio is 1x10 14 ! H 2 N NH 2 O + 2H 2 O + H + 2NH 4 + + HCO 3 -
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Some Rate Enhancements Produced by Enzymes Enzyme Enhancement Factor Cyclophilin 10 5 Carbonic anhydrase 10 7 Triose phosphate isomerase 10 9 Carboxypeptidase A 10 11 Phosphoglucomutase 10 12 Succinyl-CoA transferase 10 13 Urease 10 14 Orotidine monophosphate decarboxylase 10 17
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Enzymes are central to every biochemical process Acting in organized sequences, enzymes catalyze hundreds of stepwise reactions that degrade nutrient molecules, conserve and transform chemical energy, and make biological macromolecules from simple precursors.
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Most enzymes are proteins (exception a small group of RNA molecules are catalytic) The catalytic activity depends on the integrity of the native protein conformation. The primary, secondary, tertiary, and quaternary structures of protein enzymes are essential for their catalytic activity. structure-function relationship
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Cofactors Some enzymes require no chemical groups for activity Some enzymes require an additional chemical component called cofactor , either one or more inorganic ions or a complex organic or metallo- organic molecule called coenzyme (mostly derived from vitamin s). A complete catalytically active enzyme together with its bound coenzyme or cofactor is called holoenzyme . The protein part only is called apoenzyme or apoprotein .
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Metal Ion Enzyme Fe +2 or Fe +3 Cytochrome oxidase, Catalase, Peroxidase Cu +2 Cytochrome oxidase Zn +2 DNA polymerase, Carbonic anhydrase, Alcohol dehydrogenase Mg +2 Hexokinase, Glucose 6-phosphatase Mn +2 Arginase K +2 Pyruvate kinase Ni +2 Urease Mo Nitrate reductase Se Glutathione peroxidase Enzyme Cofactors: Some Enzymes Require Metal Ions Mostly reductase or oxidase.
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Coenzyme Entity Transferred Representative Enzyme Thiamine Pyrophosphate (TPP) Aldehydes Pyruvate dehydrogenase Flavin adenine dinucleotide (FAD) Hydrogen atoms Succinate dehydrogenase Nicotinamide adenine dinucleotide (NAD) Hydride ions (H - ) Alcohol dehydrogenase Coenzyme A (CoA) Acyl groups Acetyl-CoA carboxylase Pyridoxal phosphate (PLP) Amino groups Aspartate aminotransferase 5’-Deoxyadenosylcobalamin (vitamin B 12 ) H atoms and alkyl groups Methylmalonyl-CoA mutase Biotin CO 2 Propyonyl-CoA carboxylase Tetrahydrofolate (THF) Other one-carbon groups Thymidilate synthase Enzyme Cofactors : Some Enzymes require Coenzymes
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