Ozaki S, Kalant N
Endocrinology. 1983 Jan;112(1):381-3. doi: 10.1210/endo-112-1-381.
We have studied the suitability of the insulin-receptor complex as a substrate for hepatic lysosomal and cytoplasmic insulin-degrading enzymes. Broken lysosome preparations degraded receptor-bound insulin more slowly than free insulin; most of the degradation of bound insulin could be accounted for by prior dissociation of the complex and degradation of the freed insulin. At pH 7.6 insulin showed rapid specific and nonspecific binding to intact lysosomes; no degradation products appeared in the medium. The associated insulin could be recovered by disrupting the lysosomes or by dissociation which was rapid and complete, particularly at low pH (5.5); in both cases more than 75% of the recovered insulin was intact. Insulin did not show specific binding to lysosomal membrane, suggesting that the insulin bound to intact lysosomes was intralysosomal. Free insulin but not receptor-bound insulin was rapidly degraded by cytosolic enzymes. It is hypothesized that if receptor-bound insulin were introduced into lysosomes from endocytic vesicles it would be rapidly dissociated at the prevailing intralysosomal pH; most of the insulin would be rapidly released from the lysosomes and would be available for intracellular binding and for degradation by cytosolic insulin protease.
我们研究了胰岛素受体复合物作为肝脏溶酶体和细胞质胰岛素降解酶底物的适用性。破碎的溶酶体制剂降解与受体结合的胰岛素比游离胰岛素更慢；结合胰岛素的大部分降解可归因于复合物的预先解离和游离胰岛素的降解。在pH 7.6时，胰岛素与完整的溶酶体表现出快速的特异性和非特异性结合；培养基中未出现降解产物。通过破坏溶酶体或通过解离（特别是在低pH值（5.5）时快速且完全）可以回收相关的胰岛素；在这两种情况下，超过75%回收的胰岛素是完整的。胰岛素未显示与溶酶体膜的特异性结合，这表明与完整溶酶体结合的胰岛素是溶酶体内的。游离胰岛素而非与受体结合的胰岛素被细胞质酶快速降解。据推测，如果与受体结合的胰岛素从内吞小泡引入溶酶体，它将在溶酶体内普遍存在的pH值下迅速解离；大部分胰岛素将迅速从溶酶体中释放出来，可用于细胞内结合和被细胞质胰岛素蛋白酶降解。
