A radical carboxyl migration: The antibiotic nosiheptide, produced by Streptomyces actuosus , has high activity against multidrug-resistant pathogens. The enzymes involved in its biosynthesis include NosL, which cannibalizes tryptophan and forms a methylindolic acid precursor. Although NosL is included in a growing family of remarkable radical SAM enzymes, the mechanism by which it functions has been dif cult to identify. Using spectroscopic and theoretical approaches, Sicoli et al. show that an unexpected radical intermediate forms during the course of the reaction (see the Perspective by Bridwell-Rabb and Drennan). Unlike similar known enzymes, NosL cleaves a Cα-C bond, which results in the migration of tryptophan's carboxyl group to its side-chain indole. Science , this issue p. 1320 ; see also p. 1266

Pulsed electron–electron double resonance (PELDOR, also known as DEER) has become a method of choice to measure distances in biomolecules. In this work we show how the performance of the method can be improved at high EPR frequencies (94 GHz) using variable dual frequency irradiation in a dual mode cavity in order to obtain enhanced resolution toward orientation selection. Dipolar evolution traces of a representative RNA duplex and an α-helical peptide were analysed in terms of possible bi-radical structures by considering the inherent ambiguity of symmetry-related solutions.