1. [Pt(dien)]2+ migrates intramolecularly from methionine S to imidazole Nepsilon2 in the peptides H-His-Gly-Met-OH and Ac-His-Ala-Ala-Ala-Met-NHPh
M Hahn, D Wolters, W S Sheldrick, F B Hulsbergen, J Reedijk J Biol Inorg Chem. 1999 Aug;4(4):412-20. doi: 10.1007/s007750050327.
The pH- and time-dependent reaction of [Pt(dien)(H2O)]2+ with the methionine- and histidine-containing peptides H-His-Gly-Met-OH and Ac-His-Ala-Ala-Ala-Met-NHPh at 313 K has been investigated by HPLC and NMR spectroscopy. For both peptides, initial relatively rapid formation of the kinetically favoured methionine S-bound complex is followed by slow intramolecular migration of the [Pt(dien)]2+ fragment to imidazole Nepsilon2 (or, in the case of H-His-Gly-Met-OH, to a much lesser extent to the competing imidazole Ndelta1) of the histidine side chain over a period of 500 h. Time-dependent studies for the pentapeptide at pH 8.0 demonstrate that this isomerization can take place by either direct S-->Nepsilon2 migration or by a two-step mechanism involving initial Nepsilon2 coordination of a second [Pt(dien)]2+ fragment and subsequent cleavage of the orginal Pt-S bond in the resulting dinuclear complex. The rate of kappaS/kappaNepsilon2 isomerization is markedly reduced on lowering the pH to 5.1.
2. Cyclization of several linear penta- and heptapeptides with different metal ions studied by CD spectroscopy
M Liu, Y-C Tang, K-Q Fan, X Jiang, L-H Lai, Y-H Ye J Pept Res. 2005 Jan;65(1):55-64. doi: 10.1111/j.1399-3011.2004.00199.x.
A cyclic pentapeptide c(Tyr-Leu-Ala-Gly-Pro) (I), which was isolated and identified from Pseudostellaria heterophylla medicinal herbs, and two cyclic heptapeptides, c(Gly-Tyr-Gly-Gly-Pro-Phe-Pro) (II) and c(Gly-Ile-Pro-Tyr-Ile-Ala-Ala) (III), which were isolated and identified from Stellaria yunnanensis Franch (M), were synthesized by using 3-(diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3 H)-one (DEPBT) as a coupling reagent in solution, and mediated by different metal ions, from their linear peptide precursors H-Tyr-Leu-Ala-Gly-Pro-OH (I-1) and H-Ala-Gly-Pro-Tyr-Leu-OH (I-2), H-Gly-Tyr-Gly-Gly-Pro-Phe-Pro-OH (II-1) and H-Gly-Ile-Pro-Tyr-Ile-Ala-Ala-OH (III-1), respectively. The results show that alkali metal ions can improve the cyclization yields and/or the cyclization rates of linear peptide precursors, such as Na(+) ion is favorable for the cyclization of linear pentapeptides and Cs(+) ion is favorable for the cyclization of linear heptapeptides, while some bivalent and trivalent metal ions, such as Mg(2+), Ca(2+), Zn(2+), Fe(2+), Ni(2+) and Cr(3+) reduced/inhibited both the cyclization yields and the cyclization rates of the linear peptide precursors. The circular dichroism spectra of I-1, II-1 and III-1 with different metal ions were studied to elucidate the changes in their secondary structures. It is shown that Cs(+) can induce and stabilize the type I beta-turn conformation in the linear heptapeptide II-1 and the type II beta-turn conformation in the linear heptapeptide III-1.
3. 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.
