Institute of Biochemistry, Academy of Agriculture, Wołyńska 35, 60-637 Poznań, Poland.
Plant Physiol. 1982 Aug;70(2):344-9. doi: 10.1104/pp.70.2.344.
Inosine nucleosidase (EC 3.2.2.2), the enzyme which hydrolyzes inosine to hypoxanthine and ribose, has been partially purified from Lupinus luteus L. cv. Topaz seeds by extraction of the seed meal with low ionic strength buffer, ammonium sulfate fractionation, and chromatography on aminohexyl-Sepharose, Sephadex G-100, and hydroxyapatite.Molecular weight of the native enzyme is 62,000 as judged by gel filtration. The inosine nucleosidase exhibits optimum activity around pH 8. Energy of activation for inosine hydrolysis estimated from Arrhenius plot is 14.2 kilocalories per mole. The K(m) value computed for inosine is 65 micromolar.AMONG THE INOSINE ANALOGS TESTED, THE FOLLOWING NUCLEOSIDES ARE SUBSTRATES FOR THE LUPIN INOSINE NUCLEOSIDASE: xanthosine, purine riboside (nebularine), 6-mercaptopurine riboside, 8-azainosine, adenosine, and guanosine. The ratio of the velocities measured at 500 micromolar concentration of inosine, adenosine, and guanosine was 100:11:1, respectively. Specificity (V(max)/K(m)) towards adenosine is 48 times lower than that towards inosine.In contrast to the adenosine nucleosidase activity which is absent from lupin seeds and appears in the cotyledons during germination (Guranowski, Pawełkiewicz 1978 Planta 139: 245-247), the inosine nucleosidase is present in both lupin seeds and seedlings.
肌苷核苷酶（EC 3.2.2.2），能够将肌苷水解为次黄嘌呤和核糖的酶，已从 Lupinus luteus L. cv. Topaz 种子中通过低离子强度缓冲液提取、硫酸铵分级以及氨基己基-Sepharose、Sephadex G-100 和羟磷灰石柱层析进行了部分纯化。凝胶过滤法判断该肌苷核苷酶的天然酶分子量为 62000。该酶在 pH8 附近表现出最佳活性。从 Arrhenius 图估算的肌苷水解活化能为 14.2 千卡/摩尔。计算出的肌苷 K(m) 值为 65 微摩尔。在所测试的肌苷类似物中，以下核苷是 Lupinus 肌苷核苷酶的底物：黄苷、嘌呤核苷（星云苷）、6-巯基嘌呤核苷、8-氮杂肌苷、腺苷和鸟苷。在 500 微摩尔浓度下测量的肌苷、腺苷和鸟苷的速度比分别为 100:11:1。腺苷的特异性（V(max)/K(m)）比肌苷低 48 倍。与不存在于羽扇豆种子中且在发芽期间出现在子叶中的腺苷核苷酶活性（Guranowski、Pawełkiewicz 1978 Planta 139: 245-247）相反，肌苷核苷酶存在于羽扇豆种子和幼苗中。
