DESULFOVIRIDIN, THE DISSIMILATORY SULFITE REDUCTASE FROM DESULFOVIBRIO-DESULFURICANS (ESSEX) - NEW STRUCTURAL AND FUNCTIONAL-ASPECTS OF THEMEMBRANOUS ENZYME

Desulfoviridin from the sulfate-reducing bacterium Desulfovibrio desul furicans (Essex) is a membranous dissimilatory sulfite reductase which has been described as a alpha(2)beta(2)gamma(n) multimer (approximate to 200 kDa). The enzyme contains both siroheme and Fe/S centres in th e active site. The protein can be reconstituted into asolectin vesicle s, and the resulting proteoliposomes have been analyzed by size-exclus ion chromatography and electron microscopy. From a hydrophobicity anal ysis of the D. vulgaris enzyme which exhibits a high degree of similar ity to the dissimilatory sulfite reductase from D. desulfuricans, two putative transmembrane a-helices are postulated on each beta-subunit. Desulfoviridin catalyzes the oxidation of sulfide by cytochrome c(3) w ith a specific activity of up to 4 mu mol HS- min(-1) mg(-1) which rep resents the highest activity reported for dissimilatory sulfite reduct ases. Hereby, sulfide seems to stimulate the reaction. A model for the localization of the redox partners participating in the transformatio n of sulfite in Desulfovibrio sp. is proposed. (C) 1998 Elsevier Scien ce S.A. All rights reserved.