Caerulein-like peptides from the skin glands of the Australian Blue Mountains tree frog Litoria citropa. Part 1. Sequence determination using electrospray mass spectrometry.

Sixteen caerulein-type peptides have been isolated from the skin secretions of the Australian Blue Mountains tree frog Litoria citropa. There are four groups of these peptides. The first is based on the structure of the known neuropeptide caerulein [pEQDY(SO(3))TGWMDF-NH(2)], now renamed caerulein 1.1. Examples of peptides of the other groups are as follows: caerulein 2.1 [pEQDY(SO(3))TGAHMDF-NH(2)], caerulein 3.1 [pEQDY(SO(3))GTGWMDF-NH(2)] and caerulein 4.1 [pEQDY(SO(3))TGSHMDF-NH(2)]. All of these peptides are accompanied by the associated peptide where Phe replaces Met, and all eight of the caerulein peptides are accompanied by the desulfated analogues. Negative ion electrospray mass spectrometry (ES-MS) is used to determine the molecular weights of the caeruleins 1-4 [from their [M - H](-) ions], while the sequences of the peptides are determined from the B and Y + 2 cleavage ions in the mass spectra of the [MH(+) - SO(3)](+) ions.
(Copyright 1999 John Wiley & Sons, Ltd.)