Purification and Characterization of A Novel (<i>R</i>)-Hydroxynitrile Lyase from<i>Eriobotrya japonica</i>(Loquat)
作者:Techawaree UEATRONGCHIT、Ai KAYO、Hidenobu KOMEDA、Yasuhisa ASANO、Aran H-KITTIKUN
DOI:10.1271/bbb.80023
日期:2008.6.23
A hydroxynitrile lyase was isolated and purified to homogeneity from seeds of Eriobotrya japonica (loquat). The final yield, of 36% with 49-fold purification, was obtained by 30–80% (NH4)2SO4 fractionation and column chromatography on DEAE-Toyopearl and Concanavalin A Sepharose 4B, which suggested the presence of a carbohydrate side chain. The purified enzyme was a monomer with a molecular mass of 72 kDa as determined by gel filtration, and 62.3 kDa as determined by SDS-gel electrophoresis. The N-terminal sequence is reported. The enzyme was a flavoprotein containing FAD as a prosthetic group, and it exhibited a K m of 161 μm and a k cat⁄K m of 348 s−1 mm−1 for mandelonitrile. The optimum pH and temperature were pH 5.5 and 40 °C respectively. The enzyme showed excellent stability with regard to pH and temperature. Metal ions were not required for its activity, while activity was significantly inhibited by CuSO4, HgCl2, AgNO3, FeCl3, β-mercaptoethanol, iodoacetic acid, phenylmethylsulfonylfluoride, and diethylpyrocarbonate. The specificity constant (k cat⁄K m) of the enzyme was investigated for the first time using various aldehydes as substrates. The enzyme was active toward aromatic and aliphatic aldehydes, and showed a preference for smaller substrates over bulky one.
从枇杷(Eriobotrya japonica)种子中分离并纯化出一种羟腈裂解酶,使其达到均一性。通过30-80%(NH4)2SO4分级分离和DEAE-Toyopearl和Concanavalin A Sepharose 4B柱层析,获得了最终产率为36%、纯化倍数为49倍的酶,这表明存在一个碳水化合物侧链。纯化的酶是一个单体,通过凝胶过滤测定的分子质量为72 kDa,通过SDS-凝胶电泳测定的分子质量为62.3 kDa。报道了N-末端序列。该酶是一种含FAD作为辅基的黄素蛋白,对扁桃腈的Km值为161 μm,kcat/Km值为348 s-1 mm-1。最适pH和温度分别为pH 5.5和40 °C。该酶在pH和温度方面表现出极佳的稳定性。金属离子对其活性不是必需的,而CuSO4、HgCl2、AgNO3、FeCl3、β-巯基乙醇、碘乙酸、苯甲磺酰氟和二乙基焦碳酸酯对其活性有显著抑制作用。首次使用各种醛作为底物研究了该酶的特异性常数(kcat/Km)。该酶对芳香族和脂肪族醛均具有活性,并且对较小的底物比庞大的底物表现出偏好性。