Amino acid modifications in canine, equine and porcine pituitary growth hormones, identified by peptide-mass mapping

Modified amino acid residues in porcine, canine and equine growth hormones purified from pituitary glands were characterised by tryptic mapping and high-performance liquid chromatography with on-line coupled electrospray ionisation mass spectrometry (HPLC–ESI-MS) detection. Hormones from all three species showed the same changes. Conversion of Asp¹²⁸ to iso-Asp¹²⁸ was a component of native hormones, while deamidation of Asn¹² and Asn⁹⁸ to Asp and iso-Asp, oxidation of Met⁴, and cyclisation to the pyroglutamyl derivative of Gln¹³⁹, probably occurred in vitro, during isolation, storage or hydrolysis. Porcine and canine hormones had indistinguishable protein fingerprints, confirming the assumption, based on their cDNA sequences, that their mature primary structures are identical.