Dennis P A, Aronson N N
Biochim Biophys Acta. 1984 Mar 22;798(1):14-20. doi: 10.1016/0304-4165(84)90004-7.
The uptake and degradation of a homologous rat serum asialoglycoprotein, 125I-asialoorosomucoid, and the effects on this metabolism by leupeptin, a proteinase inhibitor, were studied in the perfused rat liver. 125I-Asialoorosomucoid was rapidly taken up by the liver (t1/2 = 5.7 min) and acid-soluble degradation products began to appear in the circulating perfusate medium after 20-30 min. These products accounted for 60-65% of the initially added radioactivity after 90 min of perfusion. The early events in the galactose-mediated uptake of 125I-asialoorosomucoid were unchanged by the presence of leupeptin. However, the appearance of acid-soluble degradation products was greatly reduced when livers had been pretreated with the inhibitor (1.0 mg for 60 min). This effect corresponded with an increase in acid-precipitable material being located within the lysosomal-rich fraction from homogenates of leupeptin-treated livers. Leupeptin inhibited degradation of 125I-asialoorosomucoid by approx. 85% relative to control values over 90 min of perfusion. Inhibition of asialoorosomucoid degradation was also demonstrated in vitro. Leupeptin (1.0 mM) reduced hydrolysis of this glycoprotein substrate by greater than 50% during a 24 h incubation with isolated lysosomal enzymes. The thiol proteinases, cathepsin B, H and L, which are known to be inhibited by leupeptin, are apparently involved in initiating digestion of rat 125I-asialoorosomucoid within liver lysosomes. As a result of inhibition by leupeptin both in the perfused liver and in vitro very limited changes occurred in the native molecular weight of the starting glycoprotein.
在灌注的大鼠肝脏中研究了同源大鼠血清去唾液酸糖蛋白（125I-去唾液酸血清类黏蛋白）的摄取和降解，以及蛋白酶抑制剂亮抑肽酶对这种代谢的影响。125I-去唾液酸血清类黏蛋白被肝脏迅速摄取（t1/2 = 5.7分钟），20 - 30分钟后酸溶性降解产物开始出现在循环灌注液中。灌注90分钟后，这些产物占最初加入放射性的60 - 65%。亮抑肽酶的存在并未改变125I-去唾液酸血清类黏蛋白在半乳糖介导摄取过程中的早期事件。然而，当肝脏用该抑制剂预处理（1.0毫克，60分钟）后，酸溶性降解产物的出现显著减少。这种效应与亮抑肽酶处理的肝脏匀浆中富含溶酶体部分的酸沉淀物质增加相对应。在90分钟的灌注过程中，亮抑肽酶使125I-去唾液酸血清类黏蛋白的降解相对于对照值大约抑制了85%。在体外也证实了亮抑肽酶对去唾液酸血清类黏蛋白降解的抑制作用。在与分离的溶酶体酶孵育24小时期间，亮抑肽酶（1.0 mM）使这种糖蛋白底物的水解减少了50%以上。已知受亮抑肽酶抑制的巯基蛋白酶组织蛋白酶B、H和L显然参与了肝脏溶酶体内大鼠125I-去唾液酸血清类黏蛋白的起始消化。由于亮抑肽酶在灌注肝脏和体外的抑制作用，起始糖蛋白的天然分子量发生了非常有限的变化。
