Institute of Chemical and Engineering Sciences, Agency for Science, Technology and Research (A STAR), 1 Pesek Road, Jurong Island 627833, Singapore.
World J Microbiol Biotechnol. 2012 May;28(5):2205-12. doi: 10.1007/s11274-012-1026-1. Epub 2012 Feb 19.
Bacillus coagulans has been of great commercial interest over the past decade owing to its strong ability of producing optical pure L: -lactic acid from both hexose and pentose sugars including L: -arabinose with high yield, titer and productivity under thermophilic conditions. The L: -arabinose isomerase (L-AI) from Bacillus coagulans was heterologously over-expressed in Escherichia coli. The open reading frame of the L-AI has 1,422 nucleotides encoding a protein with 474 amino acid residues. The recombinant L-AI was purified to homogeneity by one-step His-tag affinity chromatography. The molecular mass of the enzyme was estimated to be 56 kDa by SDS-PAGE. The enzyme was most active at 70°C and pH 7.0. The metal ion Mn(2+) was shown to be the best activator for enzymatic activity and thermostability. The enzyme showed higher activity at acidic pH than at alkaline pH. The kinetic studies showed that the K (m), V (max) and k (cat)/K (m) for the conversion of L: -arabinose were 106 mM, 84 U/mg and 34.5 mM(-1)min(-1), respectively. The equilibrium ratio of L: -arabinose to L: -ribulose was 78:22 under optimal conditions. L: -ribulose (97 g/L) was obtained from 500 g/l of L: -arabinose catalyzed by the enzyme (8.3 U/mL) under the optimal conditions within 1.5 h, giving at a substrate conversion of 19.4% and a production rate of 65 g L(-1) h(-1).
凝结芽孢杆菌由于其在嗜热条件下能够从己糖和戊糖（包括 L-阿拉伯糖）高效生产光学纯 L：-乳酸的强大能力，在过去十年中引起了极大的商业兴趣。来自凝结芽孢杆菌的 L-阿拉伯糖异构酶（L-AI）在大肠杆菌中异源过表达。L-AI 的开放阅读框包含 1422 个核苷酸，编码一个具有 474 个氨基酸残基的蛋白质。重组 L-AI 通过一步 His 标签亲和层析进行纯化至均一性。通过 SDS-PAGE 估计酶的分子量为 56 kDa。该酶在 70°C 和 pH 7.0 时最活跃。实验表明金属离子 Mn(2+)是酶活性和热稳定性的最佳激活剂。该酶在酸性 pH 下的活性高于碱性 pH 下的活性。动力学研究表明，L-阿拉伯糖转化的 K (m)、V (max) 和 k (cat)/K (m) 分别为 106 mM、84 U/mg 和 34.5 mM(-1)min(-1)。在最佳条件下，L-阿拉伯糖向 L-核酮糖的平衡比为 78:22。在最佳条件下，酶（8.3 U/mL）催化 500 g/L 的 L-阿拉伯糖转化为 97 g/L 的 L-核酮糖，底物转化率为 19.4%，产率为 65 g/L h(-1)。
