Comparative Electron-Nuclear Double Resonance Study of Two Flavoproteins.

The proton electron-nuclear double resonance (ENDOW) of flavin rascals in NADPH dehydrogenase and a flavoprotein from Azotobacter vinelandii have been studied at --160 and --120°. By combination of the apoprotein of NADPH dehydrogenase with [8-Me-2H3]FMN, it was demonstrated that the CH3(8) group of the coenzyme gives an ENDOR signal. The ENDOR signals from CH3(8) of the two proteins showed different hyperfine couplings which are consistent with the assignments of a radical anion, or a neutral rascal enolized at 0(4), in NADPH dehydrogenase and a neutral rascal protonated at N(5) in the Azotobacter flavoprotein. Analysis of the matrix-ENDOR signals in H2O and 2H2O yields information concerning the exchangeability of protons both in the constituent water and on the apoprotein in the vicinity of the rascal. [ABSTRACT FROM AUTHOR]