Charlwood P A, Regoeczi E, Hatton M W
Biochim Biophys Acta. 1979 Jun 1;585(1):61-70. doi: 10.1016/0304-4165(79)90325-8.
Asialoorosomucoid and asialofetuin were prepared by using sialidase, which was removed chromatographically before the proteins were labelled with radioactive iodine. After intravenous administration of a small amount oa asialoglycoprotein (3--4 microgram/100 g body wt.) protein-bound and non-protein radioactivities in plasmas and livers of rats were determined at intervals over a period of 30 min. Transfer of either tracer protein from plasma to liver was almost complete in 5 min. Proteolysis of asialofetuin was evident very shortly thereafter, but degradation of asialoorosomucoid commenced after a significant delay and was initially slow relative to that of asialofetuin. Studies in vitro with crude hepatic lysosomal enzyme preparations indicated that asialoorosomucoid was less readily digested than asialofetuin, and that desialylation of orosomucoid or fetuin did not noticeably increase the susceptibility of these proteins to protease action. Proteolysis of asialofetuin was also demonstrable in liver homogenates in conditions under which albumin and asialotransferrin were stable. A generalized mathematical model was devised to represent the uptake and degradation of asialoglycoproteins by the liver. The theoretical assumptions that gave the best fits with experiment are outlined and discussed.
通过使用唾液酸酶制备去唾液酸糖蛋白和去唾液酸胎球蛋白，在蛋白质用放射性碘标记之前，通过色谱法去除唾液酸酶。静脉注射少量去唾液酸糖蛋白（3 - 4微克/100克体重）后，在30分钟内每隔一段时间测定大鼠血浆和肝脏中与蛋白质结合的放射性和非蛋白质放射性。示踪蛋白从血浆转移到肝脏在5分钟内几乎完成。此后不久，去唾液酸胎球蛋白的蛋白水解就很明显，但去唾液酸糖蛋白的降解在显著延迟后才开始，并且相对于去唾液酸胎球蛋白最初较慢。用粗制肝溶酶体酶制剂进行的体外研究表明，去唾液酸糖蛋白比去唾液酸胎球蛋白更不易被消化，并且血清类黏蛋白或胎球蛋白的去唾液酸化并未显著增加这些蛋白质对蛋白酶作用的敏感性。在白蛋白和去唾液酸转铁蛋白稳定的条件下，在肝匀浆中也可证明去唾液酸胎球蛋白的蛋白水解。设计了一个通用的数学模型来表示肝脏对去唾液酸糖蛋白的摄取和降解。概述并讨论了与实验最吻合的理论假设。
