Spin Labeling in Disease

Abstract

The electron spin resonance (ESR) technique of spin labeling introduced by McConnell and co-workers (Stone et al., 1965) has been instrumental in providing molecular information about the conformation of proteins (for reviews see Morrisett, 1976; Berliner, 1978; Williams-Smith and Wyard, 1975), the structure and function of membranes [for reviews see Berliner, 1976; 1979 (and references therein); Keith et al., 1973; Smith, 1979; 1971; Ohnishi, 1976; Gaffney and McNamee, 1974; Azzi and Montecucco, 1977; Gaffney and Chen, 1977], nucleic acids (for a review see Bobst, 1979), and other biological systems (for reviews see Berliner, 1976; 1979; Swartz et al., 1972). Spin labels are stable, paramagnetic molecules that are covalently attached to or in a physical relationship with biological macromolecules or systems. In principle any stable paramagnetic species (e.g., Mn⁺², Co⁺², etc.) could be a spin label. In practice, spin labels are generally of the nitroxide type, the chemistry of which has been recently reviewed (Gaffney, 1976; Keana, 1978; 1979). The usefulness of nitroxide spin-labeling methods derives from the extreme sensitivity of ESR, the fact that opaque samples (like membranes) can be used, the molecular information about the local environment near the paramagnetic center of the spin probe that can be obtained, the relative simplicity of the resulting ESR spectra that must be analyzed, the nondestructiveness of the method, and the fact that generally, except for the spin label, the system is diamagnetic. Several general reviews of spin-labeling methods are available (McConnell and McFarland, 1970; Smith, 1972; Jost and Griffith, 1978).