Electron-spin-resonance/electron-paramagnetic-resonance spectroscopy of iron-sulphur enzymes.

The conjugated iron-sulphur proteins are enzymes that contain iron-sulphur clusters, which are paramagnetic in certain oxidation states. Numerous enzymes of this type have been isolated (Palmer, 1975; Cammack, 1979; Yoch & Carithers, 1979), and whole books have been devoted to them (Lovenberg, 1977; Spiro, 1982). Most of them (aconitase being an exception) are oxidoreductases. By using e.p.r. (see Appendix) spectroscopy, the iron-sulphur clusters can be used as probes to follow the progress of the enzyme reaction, involving substrate-binding and electrontransfer processes. E.p.r. spectroscopy can also provide information about the arrangement of the iron-sulphur clusters and other centres within the enzymes.