Andersen V, Hansen G H, Sjöström H, Norén O
Department of Biochemistry C, Panum Institute, University of Copenhagen, Denmark.
Biochim Biophys Acta. 1988 Oct 13;967(1):43-8. doi: 10.1016/0304-4165(88)90186-9.
The in vivo release of a microvillar enzyme, aminopeptidase N (EC 3.4.11.2), and a cytosolic enzyme, lactate dehydrogenase (EC 1.1.1.27), into the intestinal lumen was measured to gain information on the fraction of desquamated cell protein in intestinal juice and on the mechanism of release of intestinal microvillar enzymes. 1.6% and 2.9% of the mucosal activities of aminopeptidase N and lactate dehydrogenase were released to the intestinal lumen per hour, respectively. The ratios between aminopeptidase N and lactate dehydrogenase in intestinal perfusates and mucosal homogenates were similar. This result is compatible with the view that aminopeptidase N in the rat small intestine is predominantly released into the intestinal lumen by desquamation of enterocytes. This conclusion was supported by the failure to demonstrate microvesiculation of the microvilli by electron microscopy. 30-40% of the aminopeptidase N in the intestinal lumen is membrane-bound indicating that partial solubilization occurs during desquamation. The addition of calcium ions did not augment the release of aminopeptidase N or the membrane-bound fraction in the lumen. 10-20% of the protein content in the intestinal lumen is due to extruded cell protein. This includes aminopeptidase N which constitutes 1% of the luminal protein.
为了获取有关肠液中脱落细胞蛋白质的比例以及肠微绒毛酶释放机制的信息，对微绒毛酶氨肽酶N（EC 3.4.11.2）和胞质酶乳酸脱氢酶（EC 1.1.1.27）向肠腔的体内释放情况进行了测定。氨肽酶N和乳酸脱氢酶的黏膜活性分别以每小时1.6%和2.9%的比例释放到肠腔中。肠灌注液和黏膜匀浆中氨肽酶N与乳酸脱氢酶的比例相似。这一结果与大鼠小肠中的氨肽酶N主要通过肠上皮细胞脱屑释放到肠腔中的观点相符。电子显微镜未能显示微绒毛的微囊泡化，这支持了这一结论。肠腔中30 - 40%的氨肽酶N与膜结合，这表明在脱屑过程中发生了部分溶解。添加钙离子并未增加氨肽酶N的释放或肠腔中与膜结合部分的比例。肠腔中10 - 20%的蛋白质含量归因于挤出的细胞蛋白质。这包括占肠腔蛋白质1%的氨肽酶N。
