Pulsed ELDOR in spin-labeled polypeptides

The pulsed electron-electron double-resonance (PELDOR) technique was applied to obtain information about the structure of the synthetic polypeptide-biradical in a frozen glassy solution. From the concentration dependence of the PELDOR signal, the effects of intermolecular and intramolecular interactions were separated. It was found that the intramolecular dipole-dipole interactions in the biradical peptide led to the modulation effects in the PELDOR signal decay. This may be attributed to the existence of a conformational population having a distance between the two unpaired electrons of similar to 20 Angstrom with a distribution of (similar to 2 Angstrom). Its fraction is estimated as about 25%. (C) 1999 Elsevier Science B.V. All rights reserved.