高基質特異性L-グルタミン酸オキシダーゼより作成した基質特異性改変酵素L-アルギニンオキシダーゼの性質検討

L‒Glutamate oxidase (LGOX) from Streptomyces sp. X‒119‒6 has strict substrate specificity toward L‒glutamate. Recently, we solved the X‒ray crystal structure of LGOX and this revealed that Arg305 in the active site is the key residue involved in substrate recognition. Therefore, we created 19 mutant enzymes of R305X‒LGOX by saturation mutagenesis. One of them R305D‒LGOX, Arg305 substituted with Asp exhibited oxidase activity for L‒Arg. Optimum pH of R305D‒LGOX mutant enzyme was pH 8.5. Interestingly, the activity of R305D‒LGOX toward L‒Arg was inhibited by phosphate. And furthermore, the substrate specificity of R305D‒LGOX was affected by using buffer. The results of inhibition analysis suggest, that phosphate is a competitive inhibitor of R305D‒LGOX when L‒Arg is used as substrate. Kinetic analysis of R305D‒LGOX showed that Km value and kcat value of R305D‒LGOX toward l-Arg were 0.68 mM and 6.7 s-1 respectively. In this study, we showed that R305D‒LGOX mutant enzyme is a novel l-arginine oxidase and useful for l-arginine biosensor.