Enzymes - *ENZYMES* *ENZYMES* Definitions-Chemical...

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**ENZYMES** **ENZYMES** Definitions-- Definitions-- Chemical reactions in cells require specific catalysis. Enzymes are proteins which perform this function. Metabolite acted upon is called the enzyme’s substrate.
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A. Fundamental Properties Fundamental Properties 1) Enzymes are excellent catalysts , speeding up reactions 10 8 to 10 20 fold. They speed up reactions without being used up. 2) Specificity a) for substrate - ranges from absolute (e.g., aspartase) to relative b) for reaction catalyzed, i.e., few side-reactions and by-products, etc.) 3) Regulated-- some enzymes can sense metabolic signals.
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B. Enzymes as Molecules Enzymes as Molecules 1) Large molecules -- proteins from 12kDa - 1,000kDa or more -- most are much larger than their substrate. 2) Active site -- specific region in enzyme which interacts with its substrate. both binding and catalytic reaction occur here. some residues involved in binding substrate o thers catalyze reaction
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3) Cofactors for some reactions, the amino acids are not powerful enough for catalysis. some enzymes incorporate additional factors. metal ions as cofactors-- Zn 2+ , Fe 2+ , Cu 2+ , others coenzymes are organic cofactors prosthetic groups are covalently attached
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C. Classification of Enzymes C. Classification of Enzymes 1) named and classified according to the substrate acted upon and the reaction catalyzed. 2) trivial names-- end in -ase -- urease, hexokinase. 3) named based on a formal systemic catalog (IUB) with six major classifications. (All enzymes should fall into one of these categories and all enzymes therefore have a formal name.)
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Class 1. Oxidoreductases Oxidoreductases - catalyze redox processes Example: RCH 2 -OH RCH=O Class 2. Transferases Transferases - transfer chemical groups from one molecule to another or to another part of the same molecule. O O Example: CH 3 -C -SCoA + XR CH 3 -C -XR + HSCoA acetyl CoA acetyl group transferred
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Class 3. Hydrolases Hydrolases - cleave a bond using water to produce two molecules from one. O H 2 O O example: --CNH-R --C-OH + H 2 N-R cleavage of a peptide bond Class 4. Lyases Lyases - remove a group from or add a group to double bonds. H-X H X ---C = C--- ---C--C---
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Class 5. Isomerases Isomerases - interconvert isomeric structures by molecular rearrangements. CH 3 CH 3 HC-OH HO-CH COOH COOH Class 6. Ligases Ligases -- join two separate molecules by the formation of a new chemical bond usually with energy supplied by the cleavage of an ATP. example: O ATP ADP+P i O - OOC-C-CH 3 + CO 2 - OOC-C-CH 2 -COO - pyruvate oxaloacetate enzyme = pyruvate carboxylase
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Enzyme Mechanism Enzymes catalyze difficult reactions by changing the reaction to a series of “easier” steps including nucleophilic attack, general acid-base catalysis, covalent attachment, etc. Most common detailed example is action
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This note was uploaded on 09/18/2011 for the course BCH 4024 taught by Professor Allison during the Spring '08 term at University of Florida.

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Enzymes - *ENZYMES* *ENZYMES* Definitions-Chemical...

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