Hussein L, Elsayed S, Foda S
Nutrition and Microbial Chemistry Laboratories, National Research Center, Giza, Dokki, Egypt.
J Food Prot. 1989 Jan;52(1):30-34. doi: 10.4315/0362-028X-52.1.30.
Lactase preparations were purified from cell-free extracts of Kluyveromyces lactis to homogeneity, as determined by disc SDS polyacrylamide gel electrophoresis. A combination of techniques including ammonium sulfate or acetone precipitation and hydroxyapatite chromatography was used for the purification of the enzyme. The enzyme has a pH optimum of 6.5-7.0 with Kms' of 1.25 and 28mM for the substrates O-nitrophenylgalactopyranoside and lactose respectively. Activation energies for denaturation of enzyme and conversion of substrate to product were determined to be 15.1 and 10.0 Kcal/mol, respectively. When reconstituted skim milk containing 20% total solids was treated with the lactase preparation (60,000 lactase units/1 of milk) at 18°C, 82% of the milk lactose was hydrolyzed within 24 h. Such treatment lends itself for application in developing countries and where the incidence of lactose intolerance is high.
通过圆盘SDS聚丙烯酰胺凝胶电泳测定，从乳酸克鲁维酵母的无细胞提取物中纯化得到了乳糖酶制剂，使其达到了均一性。采用了包括硫酸铵或丙酮沉淀以及羟基磷灰石色谱在内的多种技术组合来纯化该酶。该酶的最适pH为6.5 - 7.0，对底物邻硝基苯基吡喃半乳糖苷和乳糖的米氏常数分别为1.25和28mM。测定出酶变性和底物转化为产物的活化能分别为15.1和10.0千卡/摩尔。当在18°C下用乳糖酶制剂（60,000乳糖酶单位/1升牛奶）处理含20%总固体的重构脱脂牛奶时，82%的牛奶乳糖在2小时内被水解。这种处理方法适用于发展中国家以及乳糖不耐受发生率高的地区。
