Abstract
Inhibition of some vitamin B6 enzymes by carbonyl reagents, metal-chelating agents and phenylalanine derivatives has been reported. Recently, monamine oxidase inhibition by β-phenyl-isopropyl-hydrazine has also been demonstrated, but it is not clear whether monamine oxidase is related to vitamin B6 enzyme and vitamin B2 enzyme or not. In the present paper, we report on our studies, on the mechanism of inhibition of the tryptophanase (vitamin B6 enzyme) and d-amino acid oxidase (vitamin B2 enzyme) by β-phenyl-isopropyl-hydrazine.
The results were as follows ;
1) β-PIPH was found to be inhibitory on the tryptophanase, although it did not influence the inhibitory response on the d-amino acid oxidase.
2) Detailed study indicated that β-PIPH is a nonspecific, formally noncompetitive inhibitor of the tryptophanase.
3) This inhibition is achieved by the removal of cotryptophanase added to the system in vitro through nonenzymatic reaction with β-PIPH.
4) This conclusion was strengthened by the preparation and characterization of the product of the reaction between pyridoxal and β-PIPH, and its identification as a substituted pyridoxylidene-β-phenyl-isopropyl-hydrazine.
