Winkler J R, Segal H L
J Biol Chem. 1984 Feb 10;259(3):1958-62.
Swainsonine, an alpha-mannosidase inhibitor found in the Australian plant Swainsona canescens and in spotted locoweed, was tested for its effect on the degradation of endocytosed proteins in rat liver cells. The compound inhibited the release of proteolytically derived breakdown products from endocytosed glycoproteins but not from nonglycoproteins. Fifty per cent inhibition of the degradation of 125I-asialofetuin occurred at a concentration of swainsonine in the medium of 6 X 10(-7) M. In the presence of the inhibitor, there was an increased cellular accumulation of the glycoproteins corresponding quantitatively to the decreased degradation, so that total uptake was the same in the presence or absence of the inhibitor. The excess 125I-labeled material which accumulated within cells under these conditions was found entirely in the lysosomal peak on Percoll density gradient centrifugation and migrated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with a mobility indistinguishable from that of the original material. Thus, the inhibition of breakdown occurs prior to any conversion of the protein to intermediates of detectably smaller size. In contrast to the results with swainsonine, degradation of both glycoproteins and nonglycoproteins was inhibited by chloroquine and by 3-methyladenine. The findings with 3-methyladenine are in conflict with earlier reports in the literature on the effect of this compound on degradation of endocytosed proteins.
苦马豆素是一种在澳大利亚植物灰苦马豆和斑点疯草中发现的α-甘露糖苷酶抑制剂，已对其在大鼠肝细胞中对胞吞蛋白质降解的影响进行了测试。该化合物抑制了从胞吞糖蛋白中释放经蛋白水解产生的分解产物，但对非糖蛋白则无此作用。当培养基中苦马豆素的浓度为6×10⁻⁷ M时，对¹²⁵I-去唾液酸胎球蛋白降解的抑制率达到50%。在抑制剂存在的情况下，糖蛋白在细胞内的积累增加，在数量上与降解减少相对应，因此在有或没有抑制剂的情况下总摄取量是相同的。在这些条件下细胞内积累的过量¹²⁵I标记物质在Percoll密度梯度离心时完全出现在溶酶体峰中，并且在十二烷基硫酸钠-聚丙烯酰胺凝胶电泳上迁移，其迁移率与原始物质无法区分。因此，在蛋白质转化为可检测到的较小尺寸中间体之前就发生了降解抑制。与苦马豆素的结果相反，氯喹和3-甲基腺嘌呤均抑制了糖蛋白和非糖蛋白的降解。3-甲基腺嘌呤的研究结果与文献中关于该化合物对胞吞蛋白质降解影响的早期报道相矛盾。
