PRIMARY SEQUENCE, OXIDATION-REDUCTION POTENTIALS AND TERTIARY-STRUCTURE PREDICTION OF DESULFOVIBRIO-DESULFURICANS ATCC-27774 FLAVODOXIN

Flavodoxin was isolated and purified from Desulfovibrio desulfuricans ATCC 27774, a sulfatereducing organism that can also utilize nitrate a s an alternative electron acceptor. Mid-point oxidation-reduction pote ntials of this flavodoxin were determined by ultraviolet/visible and E PR methods coupled to potentiometric measurements and their pH depende nce studied in detail. The redox potential E(2), for the couple oxidiz ed/semiquinone forms at pH 6.7 and 25 degrees C is -40 mV, while the v alue for the semiquinone/hydroquinone forms (E(1)), at the same pH, -3 87 mV. E(2) varies linearly with pH, while E(1) is independent of pH a t high values. However, at low pH (<7.0), this value is less negative, compatible with a redox-linked protonation of the flavodoxin hydroqui none. A comparative study is presented for Desulfovibrio salexigens NC IB 8403 flavodoxin [Moura, I., Moura, J. J. G., Bruschi, M. and LeGall , J. (1980) Biochim. Biophys. Acta 591, 1-8]. The complete primary ami no acid sequence was obtained by automated Edman degradation from pept ides obtained by chemical and enzymic procedures. The amino acid seque nce was confirmed by FAB/MS. Using the previously determined tridimens ional structure of Desulfovibrio vulgaris flavodoxin as a model [simil arity, 48,6%; Watenpaugh, K. D., Sieker, L. C., Jensen, L. H., LeGall, J. and Dubourdieu M. (1972) Proc. Natl Acad. Sci. USA 69, 3185-3188], the tridimensional structure of D. desulfuricans ATCC 27774 flavodoxi n was predicted using AMBER force-field calculations.