CHAPTER 20: Enzymes 20.2 CLASSIFICATION. Page GENERAL CHARACTERISTICS ENZMATIC PROCESSES

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1 CAPTER 20: Enzymes Describe the general characteristics and functions of enzymes Identify the general function of cofactors Illustrate the mechanism of enzyme function Identify factors for the regulation of enzyme activity, including zymogen precursors and allosteric regulation Compare competitive and noncompetitive inhibition 20.1 GENERAL CARACTERISTICS Globular proteins that act as as catalysts in in biochemical processes CITRATE N C C REACTIN C aconitase C C C SUBSTRATE 2 C CATALYST cis-acnitate Increases reaction rate rate without itself undergoing PRDUCT any any net net change ENZMATIC PRCESSES UNCATALYZED E REACTANTS E a E a CATALYZED EFFICACY Reaction rates greatly ( ) increased SPECIFICITY Rates increased for one specific reaction or reaction class PRDUCTS REGULATIN Reaction rates can be controlled Extent of Reaction 20.2 CLASSIFICATIN Identifying suffix -ase XIDREDUCTASES xidation and reduction C 3 C C 3 C 2 TRANSFERASES Transfer of a functional group between molecules C N C C + C N + 3 Page 20-1

2 YDRLASES ydrolysis or esterification C 3 C N + (C 3 ) 3 N + (C 3 ) 3 C 3 C LYASES Addition to a double bond, or elimination to make a double bond 2 ISMERASES Isomerization P = P P ~ LIGASES (SYNTETASES) Joining or condensation of 2 molecules C + C S CoA P C C 2 C C C C S CoA 20.3 STRUCTURE: CFACTRS AND CS PRTEIN Globular polypeptide of residues called an AP if it also contains CFACTR(S) METAL INS (Mg 2+, Fe 2+, Zn 2+, Mn 2+, Ni 2+, Se 0 ) and/or CS (organic molecules water-soluble vitamins = B vitamins, etc) 20.4 MECANISM of ACTIN MDE F ACTIN E enzyme + S ES E + substrate CMPLEX enzyme Formed at active site of enzyme P product(s) AP + CFACTR(S) = L Active site is a small pocket or cleft in enzyme surface Substrate is held in active site by noncovalent interactions with amino acid side chains P ADP ATP C C P P C C ACTIVE SITE Active site shape is complementary to substrate shape Active site shape determines specificity ACTIVE SITE Specific location on on enzyme molecule where the chemical reaction is is catalyzed PSPGLYCERATE KINASE Page 20-2

3 AP CFACTR (C) L -SUBSTRATE CMPLEX PRDUCTS -SUBSTRATE CMPLEX -SUBSTRATE CMPLEX Effect of Substrate Stereoisomerism: Lactate Dehydrogenase L-LACTATE C C 3 D-LACTATE C C 3 ACTIVE SITE C Complex formed C C 3 C 3 Further Reaction Mismatch no complex SPECIFICITY F -SUBSTRATE CMPLEX LCK-AND-KEY Reaction of only one substrate is catalyzed: absolute specificity INDUCED-FIT Reaction of closely-related substrates (functional group, bond type, stereochemistry) are catalyzed salt bridge Some drugs work better than the natural substance: Morphine hydrophobic interactions -bonds Dopamine Page 20-3

4 20.5 ACTIVITY The ACTIVITY of an enzyme, its ability to increase the rate of a reaction, is reflected in its TURNVER NUMBER (mol substrate consumed/min): TURNVER Nº REACTIN Carbonic anhydrase Lactate dehydrogenase DNA polymerase 36,000,000 60, C C 3 Pyruvate Lactate Growth of DNA chains 20.6 FACTRS AFFECTING ACTIVITY CNCENTRATIN SUBSTRATE CNCENTRATIN TEMPERATURE p CNCENTRATIN Where [S] >> [E], Increased [E] leads to increased [ES] Reaction rate increases Initial Velocity [E] SUBSTRATE CNCENTRATIN Rate initially responsive to [S] V max Rate eventually reaches a maximum (V max ) V max reached when the active site of every enzyme molecule is occupied by a substrate molecule Initial Velocity [S] Page 20-4

5 p Many structural features p dependent (ex:, N 3+ ) Large deviations from p optimum irreversibly change 3-D structure Rate Enzymes most efficient at p of normal environment (ex: cellular cytoplasm p ~7) p TEMPERATURE Enzymes most efficient at temperature of normal environment (~37 C) Below optimum temperature, insufficient energy for normal reaction rate Above optimum temperature, irreversible changes in 3-D structure (3 structure destroyed) Rate T, C 20.7 INIBITIN?!@x! IRREVERSIBLE Tight, often covalent bonding at active site Not enzyme specific EX: g 2+, CN, nerve gases INIBITR REVERSIBLE Non-covalent bonding Competitve: to enzyme active site EX: sulfa drugs Non-competitve: to cofactors or on enzyme away from active site ACTIVE INACTIVE Page 20-5

6 20.8 REGULATIN F ACTIVITY Control of enzymatic processes necessary: PSITIVE ALLSTERISM ALLSTERIC ACTIVATR (MDULATR) Conserves a cell s chemical resources/ energy Stops production of excess or unwanted reaction products REGULATRY SITE ACTIVATED YES! NEGATIVE ALLSTERISM END PRDUCT INIBITIN ACTIVATR (MDULATR) Accumulation of of product promotes conversion back to to substrate REGULATRY SITE DEACTIVATED WA? LeChatelier s Principle: Chap 8 Most enzymatic reactions can proceed in in both the forward and reverse directions FEEDBACK INIBITIN ZYMGEN (PR) CNVERSIN E 1 E 2 E 3 A B C D PRTELYTIC Downstream product (D) inhibits own synthesis by by acting as as negative allosteric inhibitor of of upstream enzyme (E (E 1 ) ZYMGEN INACTIVE ACTIVE Allows transport of enzymes in inactive form Page 20-6

7 20.9 APPLICATINS FD INDUSTRY: Fermentation, polysaccharide hydrolysis ( lite beer, Beano ), meat tenderizers MEDICINE: Post-surgery replacement of enzymes, protein breakdown as surgical procedure, clinical diagnosis of pathology ANALYSIS: bioprocess monitoring, assaying serum contents, assaying pathogen or allergen proteins Page 20-7