Mechanistic studies of the flavoenzyme tryptophan 2-monooxygenase: deuterium and 15N kinetic isotope effects on alanine oxidation by an L-amino acid oxidase.
Biochemistry
; 45(51): 15844-52, 2006 Dec 26.
Article
in En
| MEDLINE
| ID: mdl-17176107
ABSTRACT
Tryptophan 2-monooxygenase (TMO) from Pseudomonas savastanoi catalyzes the oxidative decarboxylation of l-tryptophan during the biosynthesis of indoleacetic acid. Structurally and mechanistically, the enzyme is a member of the family of l-amino acid oxidases. Deuterium and 15N kinetic isotope effects were used to probe the chemical mechanism of l-alanine oxidation by TMO. The primary deuterium kinetic isotope effect was pH independent over the pH range 6.5-10, with an average value of 6.0 +/- 0.5, consistent with this being the intrinsic value. The deuterium isotope effect on the rate constant for flavin reduction by alanine was 6.3 +/- 0.9; no intermediate flavin species were observed during flavin reduction. The kcat/Kala value was 1.0145 +/- 0.0007 at pH 8. NMR analyses gave an equilibrium 15N isotope effect for deprotonation of the alanine amino group of 1.0233 +/- 0.0004, allowing calculation of the 15N isotope effect on the CH bond cleavage step of 0.9917 +/- 0.0006. The results are consistent with TMO oxidation of alanine occurring through a hydride transfer mechanism.
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Deuterium Exchange Measurement
/
Alanine
/
L-Amino Acid Oxidase
/
Mixed Function Oxygenases
Language:
En
Journal:
Biochemistry
Year:
2006
Type:
Article
Affiliation country:
United States