Terris S, Steiner D F
J Biol Chem. 1975 Nov 10;250(21):8389-98.
The binding and the velocity of degradation of 125I-insulin in the absence or presence of varying concentrations of native procline insulin were studied using isolated rat hepatocytes. At insulin concentrations ranging from 5 X 10(-11) to 10(-6) M, insulin degradation velocity showed a first order dependence on the total concentration of insulin bound at steady state. The overall reaction had an apparent rate constant of 0.030 +/- 0.011 min-1. Furthermore, the degradation of a given amount of 125I-insulin bound to cells was more rapid and extensive than the degradation of the same amount of insulin which had been newly exposed to fresh cells. Mid pretreatment of isolated hepatocytes with trypsin or chymotrypsin at concentrations of 5 to 20 mug/ml depressed to the same degree the amount of 125-I-insulin bound at steady state and the 125I-insulin degradation velocity. Peptide or protein hormones unrelated to insulin, including the oxidized A and B chains of insulin, failed to depress the amount of insulin bound or the velocity of insulin degradation when present at concentrations of 10-5 or 10-6 M. Over a wide range of concentrations, various synthetic insulin analogues and naturally occurring insulins depressed to the same degree the amount of 125I-insulin bound at steady state and the 125I-insulin degradation velocity. These observations suggest that insulin bound to hepatocyte plasma membranes is the substrate for insulin degradation by the liver.
利用分离的大鼠肝细胞，研究了在不存在或存在不同浓度天然脯氨酸胰岛素的情况下，125I - 胰岛素的结合及降解速度。在胰岛素浓度范围为5×10（-11）至10（-6）M时，胰岛素降解速度对稳态下结合的胰岛素总浓度呈一级依赖性。整个反应的表观速率常数为0.030±0.011分钟-1。此外，与新暴露于新鲜细胞的相同量胰岛素相比，结合到细胞上的一定量125I - 胰岛素的降解更快且更广泛。用浓度为5至20微克/毫升的胰蛋白酶或糜蛋白酶对分离的肝细胞进行预处理，在相同程度上降低了稳态下结合的125 - I - 胰岛素量和125I - 胰岛素降解速度。与胰岛素无关的肽或蛋白质激素，包括胰岛素的氧化A链和B链，当浓度为10-5或10-6 M时，未能降低胰岛素结合量或胰岛素降解速度。在很宽的浓度范围内，各种合成胰岛素类似物和天然胰岛素在相同程度上降低了稳态下结合的125I - 胰岛素量和125I - 胰岛素降解速度。这些观察结果表明，结合到肝细胞膜上的胰岛素是肝脏降解胰岛素的底物。
