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

The study reports on identifying modified amino acid residues in pituitary growth hormones of dogs, horses, and pigs by using advanced chemical analysis methods. The researchers found that the hormones from all three animal species underwent the same modifications.

Methodology Used

• The researchers first purified growth hormones from the pituitary glands of the three animal species.
• These hormones were then characterised by a two-part analytical process called tryptic mapping and high-performance liquid chromatography with on-line coupled electrospray ionisation mass spectrometry (HPLC-ESI-MS) detection.
• Tryptic mapping is a method used to break down proteins into peptides, while HPLC-ESI-MS is a technique used to separate and analyse compounds based on their mass and charge.

Findings

• The researchers found that growth hormones from all three species showed identical modifications. These included the conversion of Asp128 into iso-Asp128 as a component of the native (original) growth hormones.
• Furthermore, they observed deamidation, a process by which an amide group is removed from a molecule, of Asn12 and Asn98. The areas where the amide groups were removed were replaced by Asp and iso-Asp.
• Oxidation of Met4, another kind of modification, was also observed. Oxidation is a reaction that involves the loss of electrons or an increase in oxidation state.
• The last change detected was cyclisation to the pyroglutamyl derivative of Gln139. Cyclisation is a reaction that forms a ring structure within a molecule.
• The researchers pointed out that the last three modifications may have happened during sample handling, such as during the process of isolation, storage, or hydrolysis of the hormones.
• The canine and porcine hormones had similar protein fingerprints, which led the researchers to confirm the assumption that the primary structure of these hormones is identical, an assumption previously only supported by their cDNA sequences.