Cyclic peptides from Oldenlandia affinis DC. Molecular and biological properties.

A new isolation procedure for Kalata polypeptides from the tropical plant Oldenlandia affinis DC is described. Fractions were screened by thin-layer chromatography, and Van Urk positive fractions were tested for oxytocic activity in estrogenized rat uteri. By using this procedure, we were able to isolate and characterize three macrocyclic polypeptides with uterine activity.

Refined structure and metal binding site of the kalata B1 peptide.

The cyclic polypeptide kalata B1 from the African plant Oldenlandia affinis DC consists of 29 amino acid residues with three disulfide linkages. In this study we used two-dimensional NMR spectroscopy to investigate the three-dimensional structure of the peptide and to determine the disulfide connectivities. Nuclear Overhauser effects (NOEs) between neighboring beta-protons of the cysteines detected at 750 MHz provided evidence for the disulfide connectivity pattern 5-13, 17-29, and 22-27.