Key points are not available for this paper at this time.
A preliminary characterization is provided of a naturally occurring cyclic peptide with interesting and potent biological activity. A 31-residue cyclic peptide, designated cyclopsychotride A 1, was obtained from the organic extract of the tropical plant, Psychotria longipes. Compound 1 inhibited 125I neurotensin (NT) binding to HT-29 cell membranes (IC50 3 microM) and also stimulated increased levels of cytosolic Ca2+ in two unrelated cell lines that do not express NT receptors. The peptide was found to dose-dependently increase intracellular Ca2+ at concentrations ranging from 3 to 30 microM, and this response was not blocked by a known NT antagonist. Cyclopsychotride A 1 possesses three disulfide linkages and is thought to be the largest cyclic peptide isolated from a natural source. Both 1H-nmr and cd spectroscopy showed 1 to be highly structured.
Witherup et al. (Thu,) studied this question.