Hancock K R, Ealing P M, White D W
Plant Molecular Genetics Laboratory, New Zealand Pastoral Agriculture Research Institute, Palmerston North.
Br J Nutr. 1994 Dec;72(6):855-63. doi: 10.1079/bjn19940090.
Several proteins with high proportions of S-containing essential amino acids were incubated in sheep rumen fluid in vitro and their rate of digestion was examined by sodium dodecyl sulphate-polyacrylamide-gel electrophoresis. The S-rich proteins rice prolamin (10 kDa), maize zein (10 kDa) and the 3.2 kDa pumpkin (Cucurbita maxima L.) trypsin inhibitor-1 (CMTI-1) were highly resistant to rumen fluid degradation, relative to control proteins of known degradation rate (casein, bovine serum albumin (BSA) and pea (Pisum sativum) albumin-1 (PA1)). Comparison of PA1 and a recombinant N-terminal epitope-tagged PA1 indicated that addition of the epitope caused a slight increase in resistance to rumen degradation. The proteins were also incubated with a mixture of trypsin (EC 3.4.21.4) and chymotrypsin (EC 3.4.21.1). PA1, BSA and casein were hydrolysed less rapidly than rice prolamin, maize zein and CMTI-1. Digestion by these intestinal proteases appeared to be complete. Thus, the prolamin, zein and CMTI-1 proteins are suitable candidates for expression as foreign proteins in pasture plants to increase throughput and uptake of essential amino acids in sheep.
将几种含硫必需氨基酸比例较高的蛋白质在体外羊瘤胃液中孵育，并通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳检测其消化率。相对于已知降解率的对照蛋白质（酪蛋白、牛血清白蛋白（BSA）和豌豆（Pisum sativum）白蛋白-1（PA1）），富含硫的蛋白质水稻醇溶蛋白（10 kDa）、玉米醇溶蛋白（10 kDa）和3.2 kDa南瓜（Cucurbita maxima L.）胰蛋白酶抑制剂-1（CMTI-1）对瘤胃液降解具有高度抗性。PA1与重组N端表位标签化PA1的比较表明，表位的添加导致对瘤胃降解的抗性略有增加。这些蛋白质还与胰蛋白酶（EC 3.4.21.4）和胰凝乳蛋白酶（EC 3.4.21.1）的混合物一起孵育。PA1、BSA和酪蛋白的水解速度比水稻醇溶蛋白、玉米醇溶蛋白和CMTI-1慢。这些肠道蛋白酶的消化似乎是完全的。因此，醇溶蛋白、玉米醇溶蛋白和CMTI-1蛋白是作为外源蛋白在牧草植物中表达以提高绵羊必需氨基酸通量和摄入量的合适候选物。
