Colleluori D M, Morris S M, Ash D E
Temple University School of Medicine, Department of Biochemistry, Philadelphia, Pennsylvania 19140, USA.
Arch Biochem Biophys. 2001 May 1;389(1):135-43. doi: 10.1006/abbi.2001.2324.
Human type II arginase, which is extrahepatic and mitochondrial in location, catalyzes the hydrolysis of arginine to form ornithine and urea. While type I arginases function in the net production of urea for excretion of excess nitrogen, type II arginases are believed to function primarily in the net production of ornithine, a precursor of polyamines, glutamate, and proline. Type II arginases may also regulate nitric oxide biosynthesis by modulating arginine availability for nitric oxide synthase. Recombinant human type II arginase was expressed in Escherichia coli and purified to apparent homogeneity. The Km of arginine for type II arginase is approximately 4.8 mM at physiological pH. Type II arginase exists primarily as a trimer, although higher order oligomers were observed. Borate is a noncompetitive inhibitor of the enzyme, with a Kis of 0.32 mM and a Kii of 0.3 mM. Ornithine, a product of the reaction catalyzed by arginase and a potent inhibitor of type I arginase, is a poor inhibitor of the type II isozyme. The findings presented here indicate that isozyme-selectivity exists between type I and type II arginases for binding of substrate and products, as well as inhibitors. Therefore, inhibitors with greater isozyme-selectivity for type II arginase may be identified and utilized for the therapeutic treatment of smooth muscle disorders, such as erectile dysfunction.
人II型精氨酸酶位于肝外且存在于线粒体中，催化精氨酸水解生成鸟氨酸和尿素。I型精氨酸酶的作用是净生成尿素以排泄多余的氮，而II型精氨酸酶据信主要作用是净生成鸟氨酸，鸟氨酸是多胺、谷氨酸和脯氨酸的前体。II型精氨酸酶还可能通过调节一氧化氮合酶可利用的精氨酸来调控一氧化氮的生物合成。重组人II型精氨酸酶在大肠杆菌中表达并纯化至表观均一。在生理pH条件下，II型精氨酸酶对精氨酸的Km约为4.8 mM。II型精氨酸酶主要以三聚体形式存在，不过也观察到了更高阶的寡聚体。硼酸盐是该酶的非竞争性抑制剂，其Kis为0.32 mM，Kii为0.3 mM。鸟氨酸是精氨酸酶催化反应的产物，也是I型精氨酸酶的强效抑制剂，但对II型同工酶的抑制作用较弱。此处呈现的研究结果表明，I型和II型精氨酸酶在底物、产物以及抑制剂的结合方面存在同工酶选择性。因此，或许可以鉴定出对II型精氨酸酶具有更高同工酶选择性的抑制剂，并将其用于治疗平滑肌疾病，如勃起功能障碍。
