Introduction

Abstract

I warmly commend this volume, which covers the characterization of iron–sulfur proteins, molybdenum proteins, manganese-containing enzymes, cobalt-substituted enzymes, and vanadyl-substituted proteins using electron paramagnetic resonance techniques. It complements the survey of high-resolution EPR methods, iron proteins, nickel and copper enzymes, and metals in medicine that formed the basis of the previous volume, Volume 28. Readers will find it helpful to have access to both Volumes 28 and 29 in order to obtain a comprehensive overview of the contribution of EPR techniques to metal ions in biology.

While discussion of interpretive difficulties may appear to be incidental in several of the chapters, the importance of recognizing the limitations of particular EPR techniques remains important. These include spectral overlap, particularly for iron–sulfur proteins, and the challenge of the small g-anisotropy for Mo[V] and VO[IV] when seeking to use CW-EPR alone to determine metal ion coordination. Manganese EPR is always challenging, even for isolated Mn[II] ions, but even more so for the coupled systems described in Chapters 8 and 9. High-spin cobalt[II] in distorted “tetrahedral” sites involve spectra from one of the doublets formed from S = 3/2. This involves the S = 1/2 spin Hamiltonian, where the resulting “effective” g-factors are field, and thus frequency, dependent. The role and importance of pulsed methods, Davies and Mims ENDOR, ESEEM, and HYSCORE, and the underlying theoretical basis for the interpretation of the resulting data sets are explained as appropriate in context.