[Expression and characterization of a multicopper oxidase from Lactobacillus fermentum].

Biogenic amines (BAs) are low molecular weight organic compounds that present in fermented foods. Large amount of ingested biogenic amines can cause allergy or significant symptoms. Reduction of BAs by enzymatic reaction in fermented foods is one of the most efficient methods for removal of biohazard compounds and assurance food safety. In this study, the multicopper oxidase (MCO) gene in the genome of Lactobacillus fermentum was successfully cloned in Escherichia coli BL21 and expressed at 484 U/L. The recombinant MCO was purified by the immobilized metal affinity chromatography method. The optimal reaction temperature and pH for this enzyme was detected to be 50 °C and 3.5. The Km and Vmax values of the recombinant MCO was determined to be 1.30 mmol/L and 7.67×10⁻² mmol/(L·min). Moreover, this MCO dramatically degrades histamine and tyramine by 51.6% and 40.9%, and can degrade other BAs including tryptamine, phenylethylamine, putrescine, cadaverine and spermidine, and was found to be tolerant to 18% (W/V) NaCl. The recombinant MCO is also capable of degrading BAs in soy sauce. The degradation rate of total BAs in soy sauce reaches 10.6% though a relatively low level of enzyme (500 U/L) is used. Multicopper oxidase has the potential to degrade biogenic amines in fermented foods, which lays a foundation for the further application of this kind of food enzymes.生物胺是一种存在于发酵食品中的含氮小分子有机化合物，过量摄入可能引起过敏或其他不良反应。利用酶法降解是减少发酵食品中生物胺含量从而保障食品安全的有效方法之一。文中成功克隆了来源于发酵乳杆菌的多铜氧化酶基因，在大肠杆菌中表达的酶活水平为484 U/L。通过镍柱亲和层析方法获得了此多铜氧化酶的纯酶。该多铜氧化酶的最适反应温度为50 ℃，最适反应pH 为3.5，其Km 为1.3 mmol/L，Vmax 为7.67×10⁻² mmol/(L·min)。对酶的应用特性研究表明，来源于发酵乳杆菌的多铜氧化酶对18% (W/V) NaCl 有一定的耐受性，并可降解包括色胺、苯乙胺、腐胺、尸胺、组胺、酪胺和亚精胺在内的7 种生物胺。其中它对组胺和酪胺的降解能力最高，分别为51.6%和40.9%。此外，该酶对酱油中的生物胺也有普遍降解作用，使用较低酶量 (500 U/L) 时，对酱油中总胺的降解率达到10.6%。多铜氧化酶具备降解发酵食品中生物胺的潜力，为进一步实现这类食品酶的实际应用奠定基础。.