Advantages of 15N and Deuterium Spin Probes for Biomedical Electron Paramagnetic Resonance Investigations

Abstract

15N and deuterium spin labels significantly advanced the application of electron paramagnetic resonance (EPR) in the fields of biomedical science and molecular biology. Problems involving the motional dynamics of enzyme catalysis, protein/ protein interactions, and membrane structure, which heretofore could not be addressed with EPR techniques, can now be investigated with highly quantitative approaches. The remarkable improvements afforded by isotopic substitutions of 15N and deuterium are due to three factors: (1) simplification of EPR spectral line shapes by reduction in the number of peaks; (2) increased sensitivity of the spin labels as evidenced by the elevated amplitude of spectral peak heights; and (3) enhanced resolution caused by narrowing of peak widths and elimination of overlaps of peaks. These factors facilitate the accurate interpretation of EPR spectral data, particularly for structure-function studies of large proteins and membranes. The purpose of this review is to examine the extraordinary utility of the isotopically substituted spin labels by evaluation of selected EPR investigations which may have wide applicability for biomedical experimentation. Therefore, we shall not present a detailed review of recent literature, but rather outline the uses of these spin labels for structure-function studies of enzymes and for the interactions of proteins and membranes in normal and pathological states.