Kohnert K D, Hehmke B, Woltanski K P, Ulrich F E, Zühlke H
Biomed Biochim Acta. 1983;42(9):1091-101.
An islet cell tumor, characterized by proinsulin level significantly elevated above normal human pancreas, has been found to contain insulin- and glucagon-degrading activity. Examination by chromatography on Sephadex G-75 of the degradation products formed from insulin showed A chain, and B chain rich-A chain aggregate as previously found with rat pancreatic islets. There was, however, little conversion of A chain to low molecular weight components indicating that insulinoma peptidase that has been found to degrade glucagon at about pH 6.8 degraded that A chain to a markedly lower rate. In contrast to the insulin-degrading activity, which was activated by glutathione in the presence of EDTA, the peptidase activity was not affected by the thiol compound. The activity of the peptidase was markedly inhibited by chelating agents, i.e., EDTA and o-phenanthroline, whereas chymotrypsin and trypsin inhibitors, i.e., TOS-PheCH2Cl, TOS-LysCH2Cl, soybean and pancreas trypsin inhibitor were found to have no effect.
已发现一种胰岛细胞瘤，其特征是胰岛素原水平显著高于正常人类胰腺，且具有胰岛素和胰高血糖素降解活性。通过Sephadex G - 75色谱法对胰岛素形成的降解产物进行检测，结果显示有A链以及富含A链的B链聚集体，这与之前在大鼠胰岛中发现的情况相同。然而，A链向低分子量成分的转化很少，这表明已发现的在约pH 6.8时能降解胰高血糖素的胰岛素瘤肽酶降解A链的速率明显较低。与在EDTA存在下被谷胱甘肽激活的胰岛素降解活性相反，肽酶活性不受硫醇化合物影响。肽酶活性被螯合剂（即EDTA和邻菲罗啉）显著抑制，而胰凝乳蛋白酶和胰蛋白酶抑制剂（即TOS - PheCH2Cl、TOS - LysCH2Cl、大豆胰蛋白酶抑制剂和胰腺胰蛋白酶抑制剂）则没有作用。
