Electron-spin-resonance studies on flavoenzymes

Our current knowledge on the spin distribution of flavoenzyme semiquinones would suggest that it is very similar to that determined for model flavin systems. It remains for future work to establish whether this conclusion is valid for a wide range of flavoenzymes as well as for those in which the flavin has become covalently attached to the protein via the 8 alpha position. The improvement in e.s.r. instrumental capabilities, advances in ENDOR spectroscopy, and the application of other techniques such as electron spin echo spectroscopy should result in considerable new information regarding the structures and environment of flavoenzyme semiquinones. Further application of these physical approaches to flavoenzymes in which chemically modified flavins have been substituted for the 'normal' coenzyme (Massey & Hemmerich, 1980) may be particularly informative.