Describing enzymes and their additional chemical componentsProsthetic group =coenzyme or metal ion that is very tightly orcovalentlyboundtotheenzymeproteinHoloenzyme=completecatalytically activeenzymetogetherwithitsbound coenzymeand/ormetal ionsApoenzymeorapoprotein=theproteinpartofaholoenzyme
Describing enzymes and their additional chemical components Prosthetic group = coenzyme or metal ion that is very tightly or covalently bound to the enzyme protein Holoenzyme = complete catalytically active enzyme together with its bound coenzyme and/or metal ions Apoenzyme or apoprotein = the protein part of a holoenzyme
Enzymes areclassified bythereactionstheycatalyzeEnzymes are divided into seven classes, each with subclasses.based on the type of reaction catalyzedEach enzyme has a 4-part enzyme commission number (E.Cnumber)andasystematicnameMost enzymes have trivial names
Enzymes are classified by the reactions they catalyze Enzymes are divided into seven classes, each with subclasses, based on the type of reaction catalyzed Each enzyme has a 4-part enzyme commission number (E.C. number) and a systematic name Most enzymes have trivial names
International Classification ofEnzymesClass numberClass nameTypepfreaction catalyzed1OxidoreductaseTransferofelectrons(hydrideionsorHatoms)2TransferaseGroup transfer3HydrolasesHydrolysis (transferoffunctional groupstowater)4LyasesCleavage of C-C, C-O, C-N, or other bonds byelimination, leaving double bonds or rings, or additionofgroupstodoublebonds5IsomeraseTransfer of groups within molecules to yield isomericforms6LigasesFormation ofC-C,C-S, C-O,and C-N bonds bycondensationreactions coupledtocleavageofgATP orsimilarcofactor7TranslocasesMovementofmoleculesorionsacrossmembranesortheirseparationwithinmembranes
International Classification of Enzymes Class number Class name Type pf reaction catalyzed 1 Oxidoreductase Transfer of electrons (hydride ions or H atoms) 2 Transferase Group transfer 3 Hydrolases Hydrolysis (transfer of functional groups to water) 4 Lyases Cleavage of C-C, C-O, C-N, or other bonds by elimination, leaving double bonds or rings, or addition of groups to double bonds 5 Isomerase Transfer of groups within molecules to yield isomeric forms 6 Ligases Formation of C-C, C-S, C-O, and C-N bonds by condensation reactions coupled to cleavage ofg ATP or similar cofactor 7 Translocases Movement of molecules or ions across membranes or their separation within membranes
Enzyme-Catalyzed Reactions TakePlacewithintheActiveSiteactivesite=providesaspecificenvironmentinwhichagivenreactioncanoccurmorerapidlyKeyactive-siteSubstrateaminoacidresiduessubstrate=themoleculethatisboundtotheactivesite and acted upon bythe enzyme
EnzymesAffectReactionRates,NotEquilibriasimpleenzymaticreactionscanbewrittenasE+S=ES=EP=E+P (6-1)whereE,S,andPrepresentthe enzyme,substrate,and productand ES and EP are transient complexes oftheenzyme