The stability of the commercial lactase enzyme is important for the dairy industry. A destabilizing factor for neutral lactase in the enzyme preparation from Kluyveromyces lactis was investigated. We found that lactase had lower thermal stability when fragmented bands of lactase were confirmed on SDS-PAGE. After the destabilizing factor of lactase was purified, that was identified by BLAST search as a hypothetical protein in K. lactis similar to proteinase B (PRB) of Saccharomyces cerevisiae. The molecular mass of protease was estimated to be approximately 30 kDa with SDS-PAGE. The purified protease exhibited activity toward lactase and FITC-casein but not toward bovine serum albumin or milk casein. The optimal pH and temperature of the protease were 8.0 and 40 °C, respectively. The protease activity was strongly inhibited by Fe²⁺, Cu²⁺, and a serine protease inhibitor, but activated by Ca²⁺. Based on these properties, the protease was identified as PRB. Lactase fragmentation was accelerated by the addition of purified PRB to the lactase preparation and was suppressed by protease inhibitors. Thus, this is the first report to identify and characterize PRB as the unstable factor of neutral lactase in the K. lactis preparation.

商业乳糖酶的稳定性对于乳业至关重要。研究了乳酸克鲁维酵母的酶制剂中中性乳糖酶的去稳定化因子。我们发现，在SDS-PAGE上确认乳糖酶的片段带时，乳糖酶的热稳定性较低。纯化乳糖酶的不稳定因子后，通过BLAST搜索将其鉴定为类似于酵母菌中蛋白酶B（PRB）的乳酸克鲁维酵母中的一种假设蛋白。。用SDS-PAGE估计蛋白酶的分子量约为30kDa。纯化的蛋白酶对乳糖酶和FITC-酪蛋白具有活性，但对牛血清白蛋白或牛奶酪蛋白没有活性。蛋白酶的最佳pH和温度分别为8.0和40°C。蛋白酶活性受到Fe 2 ⁺，Cu ²⁺和丝氨酸蛋白酶抑制剂的强烈抑制，但被Ca ²⁺激活。基于这些性质，将蛋白酶鉴定为PRB。通过向乳糖酶制剂中添加纯化的PRB可以加快乳糖酶的裂解，并通过蛋白酶抑制剂抑制。因此，这是第一份鉴定和鉴定PRB为乳酸克鲁维酵母中中性乳糖酶不稳定因子的报告。 制备。