Digestion and absorption of bovine milk xanthine oxidase and its role as an aldehyde oxidase.
Digestion and absorption of bovine milk xanthine oxidase and its role as an aldehyde oxidase.
复制标题
牛乳黄嘌呤氧化酶的消化和吸收及其作为醛氧化酶的作用。
DOI：
10.1093/jn/106.11.1600
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发表时间：
1976
期刊：
影响因子：
--
通讯作者：
A. Clifford
中科院分区：
文献类型：
--
作者：
C. Ho;A. Clifford
酸性和肠道蛋白水解环境对牛乳黄嘌呤氧化酶（XO）活性的影响进行了测定，以评估这种酶被吸收的生物活性形式的程度。比较了叶酸对XO的抑制作用和XO对棕榈醛、硬脂醛和黄嘌呤氧化的相对亲和力。酸和胃液对XO活性的影响通过在pH范围为2至9的缓冲液中孵育纯化的酶和非纯化的酶（牛奶）来测量。新鲜胃液也与牛奶一起孵育。随着孵育混合物的pH降低至pH 6.5以下，越来越多的酶失活。低于pH 3.5时，酶完全失活。胃液，pH值与牛奶一起孵育的汁液。牛奶XO活性降低36%，当温和的孵育与等体积的胃液。均质牛奶有59%的XO活性比生牛乳。新鲜生奶XO、均质奶XO和纯化XO同样容易被酸或胃液灭活。将牛奶与胃液或胃液与胰酶孵育后，XO活性与分子量为30万道尔顿的大分子结合，未发现含活性的亚基，估计在肠内有0.00008%的XO被吸收。叶酸和别嘌呤醇在体外均抑制XO活性。别嘌呤醇的抑制作用是叶酸的3.5倍。大量过量的膳食叶酸并没有降低大鼠肝脏或肠道体内XO活性。XO对黄嘌呤的亲和力比对棕榈醛或硬脂醛底物的亲和力大得多。据估计，新鲜原料乳中100 mg XO中，均质化后剩余41 mg，27 mg进入肠道，只有20 ng作为完整酶被吸收。
The effects of acidic and intestinal proteolytic environments on bovine milk xanthine oxidase (XO) activity were determined in order to evaluate the extent to which this enzyme was absorbed in biologically active form. The inhibition of XO by folic acid and the relative affinities of XO for the oxidation of palmitaldehyde, stearaldehyde, and xanthine were compared. The effects of acid and gastric juice on XO activity were measured by incubating purified enzyme, and non-purified enzyme (milk), in buffers ranging in pH from 2 to 9. Fresh gastric juice was also incubated with milk. Increasing amounts of the enzyme were inactivated as the pH of the incubation mixture was reduced below pH 6.5. Below pH 3.5, the enzyme was completely inactivated. Gastric juice, pH juice incubated with milk. Milk XO activity was reduced 36% when mild was incubated with an equal volume of gastric juice. Homogenized milk had 59% less XO activity compared with raw molk. Fresh raw milk XO, homogenized milk XO, and purified XO were equally susceptible to inactivation by acid or gastric juice. After incubation of milk with gastric juice, or gastric juice followed by pancreatin, XO activity was associated with a macromolecule of 300,000 daltons molecular weight and subunits containg activity were not found. It was estimated that 0.00008% of the XO in the intestine was absorbed. Both folic acid and allopurinol inhibited XO activity in vitro. Allopurinol was 3.5 times more potent an inhibitor than folic acid. A large excess of dietary folic acid did not reduce rat liver or intestinal XO activity in vivo. XO had a much greater affinity for xanthine than for palmitaldehyde or stearaldehyde substrates. It was estimated that of 100 mg of XO in fresh raw milk, 41 mg remained after homogenization, 27 mg entered the intestine and only 20 ng were absorbed as intact enzyme.