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Literature summary for 1.14.13.9 extracted from

  • Beaupre, B.A.; Reabe, K.R.; Roman, J.V.; Moran, G.R.
    Hydrogen movements in the oxidative half-reaction of kynurenine 3-monooxygenase from Pseudomonas fluorescens reveal the mechanism of hydroxylation (2020), Arch. Biochem. Biophys., 690, 108474 .
    View publication on PubMed

Application

Application Comment Organism
drug development KMO has been identified as a therapeutic target for limiting neuronal damage from ischemia and specific diseases. The inhibition of KMO in vivo has synergistic neuroprotective effects that include elevation of the concentration of kynurenate, that both slows glutamate release and antagonizes NMDA receptors, reducing aberrant excitation. Inhibition of KMO also has the added benefit of halting the accumulation of specific neurotoxic and/or apoptotic metabolites, such as 3-hydroxy-L-kynurenine and quinolinic acid Pseudomonas fluorescens

KM Value [mM]

KM Value [mM] KM Value Maximum [mM] Substrate Comment Organism Structure
additional information
-
additional information evaluation of the proton inventory resulting from medium effects or specific transition states, first-order rate constants are fit to variations of the Kresge (Gross-Butler) equation, kinetic isotope effects, oxidative half-reaction in the presence of ring perdeutero-L-Kyn, stopped-flow spectrophotometric measurements, kinetics, overview. The decay of the C4a-hydroperoxyflavin results in the regeneration of the oxidized flavin. The final step of the oxidative half-reaction is then the release of 3-hydroxy-L-kynurenine from the active site which is observed as a perturbation of the oxidized absorption spectrum Pseudomonas fluorescens

Natural Substrates/ Products (Substrates)

Natural Substrates Organism Comment (Nat. Sub.) Natural Products Comment (Nat. Pro.) Rev. Reac.
L-kynurenine + NADPH + H+ + O2 Pseudomonas fluorescens
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3-hydroxy-L-kynurenine + NADP+ + H2O
-
?

Organism

Organism UniProt Comment Textmining
Pseudomonas fluorescens Q84HF5
-
-

Reaction

Reaction Comment Organism Reaction ID
L-kynurenine + NADPH + H+ + O2 = 3-hydroxy-L-kynurenine + NADP+ + H2O the mechanism of KMO is typical of class A FAH enzymes that exhibit ping-pong kinetics in which the aromatic substrate binds first, followed by NADPH and the reduction of FAD. The NADP+ formed must then dissociate prior to the addition of molecular oxygen and the commencement of the oxidative catalytic steps. The ping-pong mechanism thus facilitates the observation of the reductive and oxidative half-reactions in separate experiments by controlling the availability of the third substrate, dioxygen. The three phases observed during the oxidative half reaction are formation of the hydroperoxyflavin, hydroxylation and product release. Reaction via C4a-hydroperoxyflavin intermediate. The oxidative half-reaction is indeed the hydroxylation step and that the aromatic position C3 of L-Kyn experiences a sp2 to sp3 hybridization change for the transition state that occurs with electrophilic attack by the hydroperoxyflavin. A non-aromatic species is the immediate product of hydroxylation and that at least two solvent derived protons are in-flight during oxygen insertion to the substrate aromatic ring. A hydroxylation transition state in which two protons are shared between the proximal and distal oxygens of the C4a-hydroperoxide as the O-O bond is broken and as sp3 character is developed at the site of hydroxylation. Such a mechanism has the C4a-oxide and the diene-imine protonated simultaneously with the requisition of one these two protons from a water molecule. Proposed mechanisms of the oxidative half-reaction of KMO, detailed overview Pseudomonas fluorescens

Substrates and Products (Substrate)

Substrates Comment Substrates Organism Products Comment (Products) Rev. Reac.
L-kynurenine + NADPH + H+ + O2
-
Pseudomonas fluorescens 3-hydroxy-L-kynurenine + NADP+ + H2O
-
?

Synonyms

Synonyms Comment Organism
pfKMO
-
Pseudomonas fluorescens

pH Optimum

pH Optimum Minimum pH Optimum Maximum Comment Organism
7.5
-
assay at Pseudomonas fluorescens

pH Range

pH Minimum pH Maximum Comment Organism
additional information
-
pH dependence of the oxidative half reaction of KMORED-mNBA complex, overview Pseudomonas fluorescens

Cofactor

Cofactor Comment Organism Structure
FAD
-
Pseudomonas fluorescens
NADPH
-
Pseudomonas fluorescens

General Information

General Information Comment Organism
evolution KMO is a class A external flavoprotein aromatic hydroxylase (FAH). This class of enzymes uses the isoalloxazine ring of FAD to mediate the delivery of electrons from singlet state NADPH to the molecular oxygen ground state triplet in order to promote subsequent hydroxylation of singlet state molecules Pseudomonas fluorescens
metabolism kynurenine 3-monoxygenase (KMO) catalyzes the conversion of L-kynurenine (L-Kyn) to 3-hydroxykynurenine (3-OHKyn) in the pathway for tryptophan catabolism. The KMO active site is insulated from exchange with solvent during catalysis Pseudomonas fluorescens
additional information the structure reveals that the aniline moiety of L-Kyn is stacked roughly perpendicular to the isoalloxazine of the FAD and that the C3 of the substrate is within 4.6 A of the flavin C4a position Pseudomonas fluorescens