CONTINUOUS-WAVE ELECTRON-NUCLEAR DOUBLE-RESONANCE SPECTROSCOPY

The rapidly accelerating progress in the biological applications of electron nuclear double resonance (ENDOR) spectroscopy seen since the 1970s reflects a combination of instrumental and conceptual advances. Structural information and its functional implications have been wrested from ENDOR studies of almost all magnetic nuclei coupled to the paramagnetic centers encountered in biological molecules. ENDOR spectroscopy, with the detailed insight it offers into the local structure of a paramagnetic centers in solution and the alterations of such structure during biological function, can often complement the tremendous power of X-ray crystallography in studies of metalloproteins. Interpretation of ENDOR spectra merges intuition with analytic rigor with the limitations of the one, often surmounted by the power of the other. Sensitivity problems persist but are yielding to studies at ever higher frequencies. Fruitful exploitation of Triple resonance in studying metalloproteins has yet to be accomplished. The wide availability of the personal computer, with its dramatically increasing speed and power, has enormously facilitated processing and interpretation of spectroscopic data. A persistent difficulty is to achieve understanding of the relaxation processes and pathways governing ENDOR spectroscopy; such understanding has yet to attain the peaks achieved by other, perhaps simpler, spectoscopies. The ingenuity and resourcefulness of experimenters remain the most powerful tools in the armamentarium of ENDOR spectroscopy. © 1993, Elsevier Inc. All rights reserved.