1. beta-Lipotropin: primary structure of the hormone from the ostrich pituitary gland
R J Naudé, D Chung, C H Li, W Oelofsen Int J Pept Protein Res. 1981 Aug;18(2):138-47. doi: 10.1111/j.1399-3011.1981.tb02051.x.
The amino acid sequence of beta-lipotropin from the ostrich pituitary has been determined. It consists of 79 amino acids. The amino acid sequence has been determined as follows: H-(1)AlA-Leu-Pro-Pro-Ala-Ala-Met-Leu-Pro-(10)Ala-Ala-Ala-Glu-Glu-Glu-Glu-Gly-Gl u-Glu-(20)Glu-Glu-Glu-Gly-Glu-Ala-Glu-Lys-Glu-Asp-(30)Gly-Gly-Ser-Tyr-Arg-Met-A rg-His-Phe-Arg-(40)Trp-Gln-Ala-Pro-Leu-Lys-Asp-Lys-Arg-Tyr-(50)Gly-Gly-Phe-Met- Ser-Ser-Glu-Arg-Gly-Arg-(60)Ala-Pro-Leu-Val-Thr-Leu-Phe-Lys-Asn-Ala-(70)Ile-Val -Lys-Ser-Ala-Tyr-Lys-Lys-Gly-(79)Gln-OH. When compared with the primary structures of other known beta-lipotropins, the sequence at the NH2-terminal, beta-melanotropin and beta-endorphin portions of the molecule exhibit considerable variability.
2. Isolation and structure determination of a paralytic peptide from the hemolymph of the silkworm, Bombyx mori
S D Ha, S Nagata, A Suzuki, H Kataoka Peptides. 1999;20(5):561-8. doi: 10.1016/s0196-9781(99)00008-x.
A peptide with paralytic activity in larvae of the silkworm, Bombyx mori, was isolated from its hemolymph. Purification procedures consisted of extraction with 50% acetone, Vydac C4 reversed-phase cartridge elution and 4 steps of reversed-phase HPLC. Injection of the purified peptide into 4th instar B. mori larvae caused rapid and rigid paralysis for 2 min at a dose of 3.4 ng/larva. This paralytic peptide consists of 23 amino acid residues containing 2 cysteines with an intra-disulfide bond. The complete amino acid sequence is: H-Glu-AsnPhe-Val-Gly-Gly-Cys-Ala-Thr-Gly-Phe-Lys-Arg-Thr-Ala-Asp-G ly-Arg-Cys-Lys-Pro-Thr-Phe-OH. The relationship between structure and the biologic activity of synthetic analogs indicated that the entire amino acid sequence and the intra-disulfide bond were necessary for biological activity.
3. Fragmentation reactions of protonated peptides containing glutamine or glutamic acid
Alex G Harrison J Mass Spectrom. 2003 Feb;38(2):174-87. doi: 10.1002/jms.427.
A variety of protonated dipeptides and tripeptides containing glutamic acid or glutamine were prepared by electrospray ionization or by fast atom bombardment ionization and their fragmentation pathways elucidated using metastable ion studies, energy-resolved mass spectrometry and triple-stage mass spectrometry (MS(3)) experiments. Additional mechanistic information was obtained by exchanging the labile hydrogens for deuterium. Protonated H-Gln-Gly-OH fragments by loss of NH(3) and loss of H(2)O in metastable ion fragmentation; under collision-induced dissociation (CID) conditions loss of H-Gly-OH + CO from the [MH - NH(3)](+) ion forms the base peak C(4)H(6)NO(+) (m/z 84). Protonated dipeptides with an alpha-linkage, H-Glu-Xxx-OH, are characterized by elimination of H(2)O and by elimination of H-Xxx-OH plus CO to form the glutamic acid immonium ion of m/z 102. By contrast, protonated dipeptides with a gamma-linkage, H-Glu(Xxx-OH)-OH, do not show elimination of H(2)O or formation of m/z 102 but rather show elimination of NH(3), particularly in metastable ion fragmentation, and elimination of H-Xxx-OH to form m/z 130. Both the alpha- and gamma-dipeptides show formation of [H-Xxx-OH]H(+), with this reaction channel increasing in importance as the proton affinity (PA) of H-Xxx-OH increases. The characteristic loss of H(2)O and formation of m/z 102 are observed for the protonated alpha-tripeptide H-Glu-Gly-Phe-OH whereas the protonated gamma-tripeptide H-Glu(Gly-Gly-OH)-OH shows loss of NH(3) and formation of m/z 130 as observed for dipeptides with the gamma-linkage. Both tripeptides show abundant formation of the y(2)'' ion under CID conditions, presumably because a stable anhydride neutral structure can be formed. Under metastable ion conditions protonated dipeptides of structure H-Xxx-Glu-OH show abundant elimination of H(2)O whereas those of structure H-Xxx-Gln-OH show abundant elimination of NH(3). The importance of these reaction channels is much reduced under CID conditions, the major fragmentation mode being cleavage of the amide bond to form either the a(1) ion or the y(1)'' ion. Particularly when Xxx = Gly, under CID conditions the initial loss of NH(3) from the glutamine containing dipeptide is followed by elimination of a second NH(3) while the initial loss of H(2)O from the glutamic acid dipeptide is followed by elimination of NH(3). Isotopic labelling shows that predominantly labile hydrogens are lost in both steps. Although both [H-Gly-Glu-Gly-OH]H(+) and [H-Gly-Gln-Gly-OH]H(+) fragment mainly to form b(2) and a(2) ions, the latter also shows elimination of NH(3) plus a glycine residue and formation of protonated glycinamide. Isotopic labelling shows extensive mixing of labile and carbon-bonded hydrogens in the formation of protonated glycinamide.
