Pulsed ELDOR in spin-labeled polypeptides

The pulsed electron-electron double-resonance (PELDOR) technique was applie d to obtain information about the structure of the synthetic polypeptide-bi radical in a frozen glassy solution. From the concentration dependence of t he PELDOR signal, the effects of intermolecular and intramolecular interact ions were separated. It was found that the intramolecular dipole-dipole int eractions in the biradical peptide led to the modulation effects in the PEL DOR signal decay. This may be attributed to the existence of a conformation al population having a distance between the two unpaired electrons of simil ar to 20 Angstrom with a distribution of (similar to 2 Angstrom). Its fract ion is estimated as about 25%. (C) 1999 Elsevier Science B.V. All rights re served.