Mather I H, Sullivan C H, Madara P J
Biochem J. 1982 Feb 15;202(2):317-23. doi: 10.1042/bj2020317.
A solid-phase immunoassay was used to detect xanthine oxidase in fractions from bovine mammary glands after electrophoresis in polyacrylamide gels containing sodium dodecyl sulphate. Under these conditions the major proportion of xanthine oxidase in either mammary tissue or mild could be recovered as a protein of mol.wt. 150 000. In mammary tissue approx. 80% of the enzyme was in a soluble form and the remainder was accounted for in either 'mitochondrial' or microsomal fractions after tissue homogenization and fractionation. Affinity chromatography of either detergent-solubilized microsomal membranes or postmicrosomal supernatants on immobilized antibody to xanthine oxidase yielded a single protein that cross-reacted with antibody to the enzyme. In milk presumptive degradation products of the enzyme were detected in minor quantities with mol.wts. of 43 000 in the whey fraction and 90 000 in fat-globule membrane. Only the undegraded enzyme was present in the skim-milk membrane fraction. Xanthine oxidase is therefore synthesized and secreted as a protein with a monomeric mol.wt. of 150 000 and is not subjected to extensive proteolytic degradation during the storage of milk in mammary alveoli. The significance of the results is discussed in relation to the overall protein composition of the membranes of milk-fat globules and skim milk.
采用固相免疫分析法，对牛乳腺组织在含十二烷基硫酸钠的聚丙烯酰胺凝胶中电泳后的各组分进行黄嘌呤氧化酶检测。在这些条件下，乳腺组织或乳汁中大部分黄嘌呤氧化酶可作为分子量为150000的蛋白质回收。在乳腺组织中，约80%的酶呈可溶形式，其余部分在组织匀浆和分级分离后存在于“线粒体”或微粒体组分中。用固定化的抗黄嘌呤氧化酶抗体对去污剂增溶的微粒体膜或微粒体后上清液进行亲和层析，得到一种与该酶抗体发生交叉反应的单一蛋白质。在乳汁中，检测到该酶的少量推定降解产物，乳清组分中的分子量为43000，脂肪球膜中的分子量为90000。脱脂乳膜组分中仅存在未降解的酶。因此，黄嘌呤氧化酶是以分子量为150000的单体形式合成并分泌的，在乳腺泡中储存乳汁的过程中不会受到广泛的蛋白水解降解。结合乳脂肪球膜和脱脂乳的整体蛋白质组成对结果的意义进行了讨论。
