Nitrogen assimilationMoving amino groupsTransaminationreactions Transfer aminegroups between moleculesAmino acid-A + keto acid-B → Amino acid-B + Keto acid-ASpecialcofactorrequired:PLPOHOHCHPyridoxal-s'.Pyridoxinephosphate(PLP)(vitaminBe)吡哆醛
吡哆醛 Nitrogen assimilation Moving amino groups Transamination reactions Transfer amine groups between molecules • Amino acid-A + keto acid-B ← → Amino acid-B + Keto acid-A Special cofactor required: PLP
TransaminasemechanismPyridoxal-5'-phosphate (PLP) carries aldehyde groupNo such group on amino acid side chainInitially covalently bound to enzyme via Lys side chain (c-amino)OHOH10.HOCH,CHHHPyridoxal-5'Pyridoxinephosphate(PLP)(vitaminBe)
Transaminase mechanism Pyridoxal-5’-phosphate (PLP) carries aldehyde group No such group on amino acid side chain Initially covalently bound to enzyme via Lys side chain (ε-amino)
Transaminase mechanismEnzyme(CH2)aCOOGeneralstepsofmechanismNHHN Amino acidbindsfirst-need amine donorAminoacid Forms SchiffbasewithPLPviaα-aminegroup Breaks bond with Lys1Enzyme-PLpSchiffbaseHEnzymeCOO(CH,)4NHHHAminoacid-PLPSchiffbase
Transaminase mechanism General steps of mechanism Amino acid binds first – need amine donor Forms Schiff base with PLP via α-amine group Breaks bond with Lys
Transaminase mechanismStepsofmechanism酮亚胺Several chemical stepsleadtohydrolysisofketimineintermediateand release of keto acid product PDX (pyridoxamine): amine group now on PLP吡哆胺EnzYmeEnzyme-CO0H,NH.NNH-COOa-KetoacidH,O40.PCHKetimine
酮亚胺 吡哆胺 Transaminase mechanism Steps of mechanism Several chemical steps lead to hydrolysis of ketimine intermediate and release of keto acid product PDX (pyridoxamine): amine group now on PLP
Transaminase mechanismSteps ofmechanismKetoacidsubstratebinds Amine group transferred fromPLPtoketo acidEnryme-PLSchiffbase Form amino acid and regeneratePLP-Lys(CHlNH,oacid-PLPSchiffbaseCWKetiminH.OH.IcOOa-Ketoacid20,PO
Transaminase mechanism Steps of mechanism Keto acid substrate binds Amine group transferred from PLP to keto acid Form amino acid and regenerate PLP-Lys