抄録
An attempt to characterize the amino acid residue of the terminal and internal bond in uremic peptide chains by enzymatic digestion and chemical hydrolysis after dansylation was made. Thirteen uremic peptides chosen from two groups of 36 uremic peptids which had been obtained from hydrophobic middle molecule fraction in hemofiltrates of previously reported two dialysis patients, were reacted with 8 kinds of proteases. The result of enzymatic digestion revealed that these peptide chains were hardly cleaved with the following enzymes; CPase B (EC 3.4.12.3), pyroglutamate aminopeptidase (EC 3.4.11.8), trypsin (EC 3.4.21.4), chymotrypsin (EC 3.4.21.2) and papain (EC 3.4.22.2). Only one residue of each terminal amino acid of 3 uremic peptide chains was slightly released by the action of CPase A (EC 3.4.12.2) or Y and LAP (EC 3.4.11.2), whereas the sequential release of amino acids was not observed. Although only α-amino terminal residue of 10 uremic peptides as dansylamino acids was produced by chemical hydrolysis after dansylation and ε-amino-dansyl lysine was undetectable in the hydrolysate of the peptide chain including lysine residue, results indicate possibility of the modification of theε-amino group of lysine in the chain. On the other hand, it was also clarified these uremic peptides have no inhibitory effect against protease. These results suggest that there are possible modifications on the amino acid residues in uremic peptide chains which lower hydrophobicity and hinder the conjugation with plasma components or enzyme proteins. This undigestable character in itself may lead to the retention of uremic peptides in blood circulation.
