Degradation of insulin and insulin-like growth factors by enzyme purified from human erythrocytes. Comparison of degradation products observed with A14- and B26-[125I]monoiodoinsulin.
An insulin-degrading enzyme has been purified from human erythrocytes. This enzyme degraded 125I-labeled insulin-like growth factor I (IGF-I) more slowly than 125I-IGF-II and degraded IGF-II more slowly than 125I-insulin. The time course of 125I-insulin degradation suggested the presence of intermediates, each of which was itself shown to be a substrate for the enzyme. One of these intermediates appeared to be made up entirely of B-chain residues and had HisB10 as its NH2-terminal. The final major radiolabeled degradation product of A14-[125I]monoiodoinsulin was a peptide with TyrA14 at the A-chain NH2 terminal. This peptide could be reduced with dithiothreitol, suggesting that it contained amino acid residues from both A- and B-chains. It was partially precipitated by trichloroacetic acid and anti-insulin antibody but bound poorly to IM-9 lymphocytes. The final major degradation product of B26-[125I]monoiodoinsulin was a peptide whose NH2-terminal was TyrB26 and could not be reduced by dithiothreitol. It was partially precipitated by anti-insulin antibody but was precipitated poorly, if at all, by trichloroacetic acid and bound poorly to IM-9 lymphocytes. The results show that this enzyme degraded insulin by sequential cleavage of peptide bonds on both A- and B-chains. We identified LeuA13-TyrA14, SerB9-HisB10, and PheB25-TyrB26 as three of the bonds that are cleaved.
Misbin
R I
RI
Division of Endocrinology and Metabolism, University of Florida College of Medicine, Gainesville 32610.
Almira
E C
EC
D002850:Chromatography, Gel; D004912:Erythrocytes / Q000201:enzymology*; D006801:Humans; D007328:Insulin / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000097:blood*; D007335:Insulin-Like Growth Factor II / Q000097:blood*; D007339:Insulysin / Q000097:blood*; D007457:Iodine Radioisotopes; D007700:Kinetics; D010446:Peptide Fragments / Q000302:isolation & purification; D010447:Peptide Hydrolases / Q000097:blood*; D011865:Radioisotope Dilution Technique; D013002:Somatomedins / Q000097:blood*; D013379:Substrate Specificity
D007328:Insulin; D007457:Iodine Radioisotopes; D010446:Peptide Fragments; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D010447:Peptide Hydrolases; D007339:Insulysin