Speciation 98: Abstracts

Pituitary adenylate cyclase activating polipeptide (PACAP) was isolated from ovine hypothalamic tissue as a 38-amino acid amidated peptide-PACAP (1-38) and PACAP (1-27) corresponding to the N-terminal 27 residues of PACAP (1-38). They are derived from 175 amino acid precursor. PACAP is not only a hypothalamic hormone but it seems to have a much wider spectrum of physiological functions. PACAP stimulates adenylate cyclase, mobilises intracellular Ca²⁺ and causes the secretion of insulin from pancreas and catecholamines from adrenal chromaffin cells.

The results of the present studies on the complexes formed by the PACAP fragments: PACAP1 (1-5) His-Ser-Asp-Gly-Ile-NH₂, PACAP2 (7-11) Thr-Asp-Ser-Tyr-Ser-NH₂ and PACAP3 (14-27) Arg-Lys-Gln-Met-Ala-Val-Lys-Lys-Tyr-Leu-Ala-Ala-Val-Leu-NH₂ with H⁺ and Cu²⁺ are reported in this work. The metal-peptide systems were studied in aqueous solution using a combination of pH-metric titrations and absorption CD and EPR. spectro-scopy.

The PACAP1 forms with Cu²⁺ ions the CuLH, CuL, CuLH_-2, CuLH_-3 and Cu₂L₂H_-2 complexes. The presence of dimer species was confirmed by spectroscopic studies. The EPR spectra were silent in the pH regions over which the existence of dimeric species had been found with the speciation calculations based on the potentiometric data. CD spectra with the N_imd Cu²⁺ charge transfer band at 340 nm clearly indicated the involvement of imidazole nitrogen in metal ion co-ordination.

PACAP2 forms the CuLH, CuL, CuLH_-1, CuLH_-2 and CuLH_-3 complexes. The CuL complex (2N) is presented in the wide pH range (4.5-8) due to binding of Asp²-b-carboxylate group. However, it does not prevent complete deprotonation and binding of the second and third peptide nitrogens to give 3N (CuLH_-1) and 4N (CuLH_-2, CuLH_-3) complexes at higher pH.

The tetradecapeptide PACAP3 forms with Cu²⁺ unusually stable 4N complex.

Back to the list of abstracts