Purification of large neuromedin N (NMN) from canine intestine and its identification as NMN-125.

A large molecular form of neuromedin N (NMN), a neurotensin (NT)-related peptide, was purified to homogeneity from canine ileal mucosa. The amino acid sequence of its N-terminal 20 residues was found to be SDSEEEMKALEADLLTNMHT, which is identical to residues 24-43 of the cDNA-predicted NT/NMN precursor. Prior work had indicated that the NMN moiety was located at the C-terminus of large NMN. Having now defined both the N-terminus and C-terminus of large NMN, we note that this molecule must be comprised of 125 amino acids (including residues 24-148 of prepro NT/NMN) and we suggest that it be named NMN-125. This information also defines the signal peptide cleavage site as the cysteine-serine bond within the precursor. The amino acid composition of the isolated peptide and its molar extinction coefficient for absorbance at 280 nm were similar to those for the 24-148 segment of prepro NT/NMN. However, the empirically determined molecular weight (17 kDa) and the isoelectric point (pI = 5.4) were slightly higher than those predicted solely from the peptide's amino acid content (14.43 kDa and pI = 4.65, respectively). In total, these results indicate that the major NMN-related peptide found in canine ileum is 125 residues in length, extending from the putative signal peptide to the C-terminus of NMN, and that it might contain non-amino acid substituents.