|
type |
Journal Article |
authors |
Tanizawa, K.; Soda, K. |
title |
The mechanism of kynurenine hydrolysis catalyzed by kynureninase |
journal |
J Biochem (Tokyo) |
Activity |
3.7.1.3 |
ui |
80094355 |
year |
(1979) |
volume |
86 |
number |
5 |
pages |
1199-209. |
| |
keywords |
Hydrolases/*metabolism |
abstract |
Several kynurenine analogs have been prepared and examined for their susceptibility to hydrolytic cleavage by bacterial kynureninase. In addition to L-kynurenine, 4-fluoro- and 5-fluoro-L-kynurenines were hydrolyzed rapidly. 3-Hydroxy-, 5-hydroxy-, 5-methyl-, and N'-formyl-L- kynurenines, and beta-benzoyl-DL-alanine were hydrolyzed slowly, whereas D-kynurenine, S-benzyl-L-cysteine, and L-asparagine were not hydrolyzed. Kinetic parameters for these kynurenine analogs indicate that a substituent on the benzene ring of kynurenine does not greatly affect the affinity of the enzyme for the substrate but does markedly affect the rate of hydrolysis. gamma-(o-Aminophenyl)-L-homoserine was converted into L-alanine and o-amino-benzaldehyde, suggesting that the sigma-bond electrons between the beta- and gamma-carbon atoms of this kynurenine analog remain in the alanyl moiety during the enzyme reaction. Aromatic compounds such as o-aminobenzaldehyde and o- aminoacetophenone strongly inhibited the kynurenine hydrolysis. It was shown that kynurenic acid is not produced by kynureninase by the use of isotopically labeled substrate. A small amount of pyruvate was definitely formed in the kynureninase reaction. On the basis of these results, a reaction mechanism is proposed for the enzymatic kynurenine cleavage, involving hydrolysis of the alpha, gamma-diketone intermediate to give anthranilic acid and the pyruvate-pyridoxamine 5'- phosphate Schiff base, which is further converted into the alanine- pyridoxal 5'-phosphate Schiff base, or directly hydrolyzed to give pyruvate and the pyridoxamine 5'-phosphate form of the enzyme. |
last changed |
2002/11/12 16:17 |
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