ENDOR studies of flavins and flavoproteins

Abstract

Electron nuclear double resonance (ENDOR) studies have been performed on the different radical states of flavin model compounds in isotropic fluid solution, in reversed micelles and in frozen solution. Sets of hyperfine coupling constants were evaluated, allowing conclusions about the influence of different substituents on the spin-density distributions within the isoalloxazine ring system. It was shown that reversed micelles offer a very promising approach to overcome the stability problems often met with flavin radicals. Powder-type ENDOR spectra have been obtained from the radical states of a variety of flavoproteins. It was demonstrated that information about enzyme–substrate interactions is accessible since these interactions cause spin-density redistributions which are reflected in changes of the hyperfine data.