1.Neurotensin modulates the electrical activity of frog pituitary melanotropes via activation of a G-protein-coupled receptor pharmacologically related to both the NTS1 and nts2 receptors of mammals.
Belmeguenai A1, Vaudry H, Leprince J, Vivet B, Cavelier F, Martinez J, Louiset E. Neuroendocrinology. 2000 Dec;72(6):379-91.
The primary structure of frog neurotensin (fNT) has recently been determined and it has been shown that fNT is a potent stimulator of alpha-MSH secretion by frog pituitary melanotropes. In the present study, we have investigated the effects of fNT on the electrical activity of cultured frog melanotropes by using the patch-clamp technique and we have determined the pharmacological profile of the receptors mediating the effect of fNT. In the cell-attached configuration, fNT (10(-7) M) provoked an increase in the action current discharge followed by an arrest of spike firing. In the gramicidin-perforated patch configuration, fNT (10(-7) M) induced a depolarization accompanied by an increase in action potential frequency and a decrease in membrane resistance. Administration of graded concentrations (10(-10) to 10(-6) M) of fNT or the C-terminal hexapeptide NT(8-13) caused a dose-dependent increase in the frequency of action potentials with EC(50) of 2 x 10(-8) and 5 x 10(-9) M, respectively.
2.Characterization of folded conformations in a tetrapeptide containing two tryptophan residues by vibrational circular dichroism.
Petrovic AG1, Polavarapu PL, Mahalakshmi R, Balaram P. Chirality. 2009;21 Suppl 1:E76-85. doi: 10.1002/chir.20779.
The intramolecularly hydrogen bonded conformations of the tetrapeptide Boc-Trp-Aib-Gly-Trp-OMe (WUGW) are investigated using experimental and quantum chemical predictions of vibrational circular dichroism (VCD) in the 1800-1550 cm(-1) region. The predicted VCD spectrum, for a conformation (conformer A) obtained from optimization of crystal structure, reproduced the dominant negative VCD band observed experimentally in CH(3)OH and CHCl(3) solvents. However, the predicted VCD spectrum of Conformation A also has an extra positive band which is not seen in the experimental spectra. This mismatch appears to be due to the lack of solvent influence in the quantum chemical geometry optimizations. However, Conformations I and II, obtained, respectively, from constrained optimization of crystal and NMR structures, mimic the solvent stabilized structures and are predicted to have dominant negative VCD band as found in the experimental spectra. It is noted that, for the peptide investigated here, unconstrained quantum chemical geometry optimizations in vacuum converged to structures that are not the realistic models of conformations found in solution.
