D型氨基酸氧化酶活性对于D-硝基精氨酸手性转化的影响

D-硝基精氨酸(D-NNA)可在大鼠体内发生手性转化生成其L型异构体,即L-NNA,后者可抑制一氧化氮合酶活性,减少一氧化氮生成,升高动脉血压.研究了D型氨基酸氧化酶(DAAO)在D-NNA手性转化中的作用及DAAO对不同(包括已报道在体内可发生手型转化的)D型氨基酸的选择活性.体内实验显示,DAAO的选择性抑制剂苯甲酸钠(400mg/kg)或肌酐(400mg/kg)均可在不同程度上抑制D-NNA升压作用,进一步研究发现,肾脏或肝脏DAAO酶液在外加DAAO后可提高D-NNA的手性转化约2倍,表明DAAO对于D-NNA在体内的手性转化是必需的.DAAO酶液对可在体内发生手性转化且转化率相似(30%～50%)的D型氨基酸(D-Phe,D-Leu和D-NNA)的选择性表现出显著差异(Kcat/Km相差可达约15倍左右),这从另一方面表明体内D-硝基精氨酸氧化是其发生手性转化的前提条件但非决定因素.

Effects of D-Amino Acid Oxidase on Chiral Inversion of NG-nitro-D-arginine

NG-nitro-D-arginine (D-NNA) produced pressor responses in rats by acting via chiral inversion intoNG-nitro-L-arginine (L-NNA), an inhibitor of nitro oxide synthase. The present investigation aimed to study the roleof the D-amino acid oxidase (DAAO) in chiral inversion of D-NNA and the relationship between DAAO activitieson various D-amino acids and their inversion rate. Benzoate (400 mg/kg) or creatinine (400 mg/kg), two inhibitorsof DAAO, blocked D-NNA-induced pressor responses in rats. Furthermore, the addition of the pure DAAOsignificantly potentiates L-NNA production rate in kidney homogenates by approximately 2-folds. The in vivo andin vitro results suggested that DAAO plays an essential role in the pressor responses elicited by D-NNA.Moreover, crude DAAO solution from the kidney showed marked selection (the maximal ratio of Kcat/Km wasnearly 15 times) on different D-amino acids that exhibited similar chiral inversion rate in vivo, suggesting that otherenzymes, such as transaminase, are also required for the entire process of D-NNA chiral inversion.