[Hormone-receptor-relationships: synthesis and characteristics of N-epsilon-dansyllysine 21-adrenocorticotropin-(1-24)-tetrakosipeptide]

Highly potent fluorescent analogues of the opioid peptide [Dmt1] DALDA

H-Dmt-D-Arg-Phe-Lys-NH2 (Dmt=2',6'-dimethyltyrosine) ([Dmt1] DALDA) is a highly potent and selective micro opioid peptide agonist capable of producing an antinociceptive effect after systemic administration. Fluorescent analogues of [Dmt1] DALDA containing either beta-dansyl-L-alpha,beta-diaminopropionic acid [Dap(dns)] or beta-anthraniloyl-L-alpha,beta-diaminopropionic acid [Dap(atn)] in place of Lys4 were synthesized. Both analogues retained subnanomolar mu opioid receptor binding affinity, very high mu opioid agonist activity in the guinea pig ileum assay and extraordinarily high antinociceptive activity in the mouse tail-flick test (intrathecal administration). The maxima of the fluorescence emission spectra recorded in Tris-HCl buffer (pH 6.6) indicated a completely aqueous environment of the fluorophore in both peptides. The high fluorescence quantum yield (phi=0.358) of the [Dap(atn)4] analogue was particularly remarkable. These fluorescent [Dmt1] DALDA analogues represent valuable pharmacological tools for various applications, including studies on the binding to receptors and other biopolymers, cellular uptake and intracellular distribution, and tissue distribution.

Study of adrenocorticotropic hormone conformation by evaluation of intramolecular resonance energy transfer in N -dansyllysine 21 -ACTH-(1-24)-tetrakosipeptide

The solution conformation of ACTH was studied by intramolecular resonance energy transfer and fluorescence depolarization with the synthetic, biologically active, derivative N(epsilon)-dansyllysine(21)-ACTH-(1-24)-tetrakosipeptide. The Förster parameters involved in energy transfer from the donor Trp(9) to the dansyl acceptor attached to the side chain of Lys(21) were determined from measurements with ACTH fragments containing either the donor or the acceptor alone. From determinations of the fluorescence quantum yields of the donor in the derivative and in the native ACTH-(1-24)-tetrakosipeptide, it was shown that besides energy transfer no additional quenching of the donor fluorescence is introduced by the presence of the acceptor. The short measured rotational relaxation time of the dansyl chromophore reflects the flexibility of the lysine side chain and justifies the use of an average value for the orientation factor in the distance calculations. The calculated intramolecular distance is remarkably independent of solvent, indicating a "random coil" situation with regard to residues 9-21.