lecture_15a - Enzyme Catalysis General Properties of...

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Enzyme Catalysis 3/17/2003
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General Properties of Enzymes Increased reaction rates sometimes 10 6 to 10 12 increase Enzymes do not change G just the reaction rates. Milder reaction conditions Great reaction specificity Can be regulated
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Substrate specificity The non-covalent bonds and forces are maximized to bind substrates with considerable specificity Van der Waals forces electrostatic bonds (ionic interactions) Hydrogen bonding Hydrophobic interaction A + B P + Q Substrates Products enz
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+ + + + + H NADH CH CH NAD OH CH CH 3 2 3 O Enzymes are Stereospecific Yeast Alcohol dehydrogenase
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N C H NH 2 O + CH 3 C D OH + N C H NH 2 O D CH 3 C- D O + Pro- R hydrogen gets pulled off Ox. Red. NADD NAD + Yeast Alcohol dehydrogenase
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2. NAD D + CH 3 -C-H O C H D OH CH 3 C H D OH CH 3 3. CH3-C -D + NADH O If the other enantiomer is used, the D is not transferred YADH is stereospecific for Pro -R abstraction
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Both the Re and Si faced transfers yield identical products. However, most reactions that have an Keq for reduction >10 -12 use the pro -R hydrogen while those reactions with a Keq <10 -10 use the pro -S hydrogen. The reasons for this are still unclear
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Specific residues help maintain stereospecificity Liver alcohol dehydrogenase makes a mistake 1 in 7 billion turnovers. Mutating Leu 182 to Ala increases the mistake rate to 1 in 850,000. This is a 8000 fold increase in the mistake rate, This suggests that the stereospecificity is helped by amino acid side chains .
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Geometric specificity Selective about identities of chemical groups but Enzymes are generally not molecule specific There is a small range of related compounds that will undergo binding or catalysis.
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Similar shaped molecules can be highly toxic N C H NH 2 O + N N CH 3 Tobacco Nicotine Because of this closeness in name Nicotinic acid was renamed to niacin by the bread manufactures
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Coenzymes Coenzymes: smaller molecules that aid in enzyme chemistry. Enzymes can: a. Carry out acid-base reactions b. Transient covalent bonds c. Charge-charge interactions Enzymes can not do: d. Oxidation -Reduction reactions e. Carbon group transfers Prosthetic group - permanently associated with an enzyme or transiently associated. Holoenzyme: catalytically active enzyme with cofactor. Apoenzyme: Enzyme without its cofactor
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Commom Coenzymes Coenzyme Reaction mediated Biotin Carboxylation Cobalamin (B12) Alkylation transfers Coenzyme A Acyl transfers Flavin Oxidation-Reduction Lipoic acid Acyl transfers Nicotinamide Oxidation-Reduction Pyridoxal Phosphate Amino group transfers Tetrahydrofolate One-carbon group transfers Thiamine pyrophosphate Aldehyde transfer
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Vitamins are Coenzyme precursors Vitamin Coenzyme Deficiency Disease Biotin Biocytin not observed Cobalamin (B 12 ) Cobalamin Pernicious anemia Folic acid tetrahydrofolate Neural tube defects Megaloblastic anemia Nicotinamide Nicotinamide Pellagra Pantothenate Coenzyme A Not observed Pyridoxine (B 6 ) Pyridoxal phosphate Not observed Riboflavin (B2) Flavin Not observed Thiamine (B 1 ) Thiamine pyrophosphate Beriberi
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These are water soluble vitamins. The Fat soluble
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This note was uploaded on 02/22/2011 for the course BCHS 3304 taught by Professor Johnson during the Spring '08 term at University of Houston.

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lecture_15a - Enzyme Catalysis General Properties of...

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