Abstract: Nicotinic acid biotransformation by immobilized Gibberella intermedia CA3-1 harboring nitrilase was investigated in this study. Chitosan-polyvinyl alcohol was found to exhibit great advantages over other composite materials，with contents of chitosan and polyvinyl alcohol 1.6% and 2%，respectively. The experimental results showed that the optimal transformation conditions were as follows：initial 3-cyanopyridine concentrations of 300mmol/L，transformation temperature of 30℃ and initial pH of 7.0. The substrate could be completely converted within 60min. Immobilized cells could be reused for up to 26 batches as compared to 9 batches for free cells. And 283.5g nicotinic acid/(g dcw) was produced with 80.55% enzyme activity preserved. Its transformation capability was three times higher than that of free cells. In addition，the immobilization substantially enhanced its tolerance toward high 3-cyanopyridine concentration and improved its thermalstability. Immobilized cells could biosynthesize 191.3g nicotinic acid/(g dcw)，retaining 30% enzyme activity by 19 fed-batches.

Key words: nicotinic acid, G. intermedia CA3-1, immobilization, biocatalysis, stability

摘要： 研究不同复合包埋材料对含腈水解酶的Gibberella intermedia CA3-1进行固定化，选择出最为适合的壳聚糖-聚乙烯醇作为复合包埋材料，其优化后的浓度分别为1.6%和2%。实验结果表明该固定化细胞的最适转化条件为：3-氰基吡啶初始浓度300mmol/L，转化温度30℃，pH值7.0，转化时间60min。固定化细胞可以稳定进行26个批次转化，每克干细胞可转化产生283.5g烟酸，为游离细胞的3倍。此外，固定化细胞对高浓度3-氰基吡啶的耐受性大幅提高，温度稳定性有一定增强。连续补料19次，固定化细胞酶活保留约30%，经折算产率为每克干细胞转化生成191.3g烟酸。

关键词: 烟酸, G. intermedia CA3-1, 固定化, 生物催化, 稳定性