Characterization of a dissimilatory-type sulfite reductase, desulfoviridin, from Desulfovibrio africanus Benghazi.

Abstract

A desulfoviridin-type sulfite reductase having the alpha band at 638 nm was purified from Desulfovibrio africanus Benghazi (NCIB 8401) by chromatography on DEAE-cellulose, Sephadex G-200, and DEAE-Sepharose columns and by disc gel electrophoresis. The content of desulfoviridin in the soluble protein was estimated to be about 6% from the purification indexes. Like the typical desulfoviridin from D. vulgaris Miyazaki K, it formed mainly trithionate besides thiosulfate and sulfide in sulfite reduction coupled to hydrogenase and methyl viologen. No significant differences in the amino acid compositions, CD patterns in the UV (205-250 nm) region, and subunit structures were found, except for a pI value about 1 unit larger (pI 5.3). The split Soret (410 +/- 2 nm, less intense peak at 391 +/- 2 nm with a shoulder around 380 nm) and beta (584 +/- 2 nm) band maxima of the enzyme as isolated, and the visible absorption and fluorescence spectra of the acidic acetone-extracted chromophore were almost identical to those ascribed to sirohydrochlorin in spite of the reported difference in the native enzyme (alpha band maxima at 638 nm as against 628 +/- 2 nm in a typical desulfoviridin). Iron was the only significant chelatable metal contained in the chromophore. Some differences between africanus and vulgaris desulfoviridins were observed in the CD patterns in the UV to near UV region (250-340 nm) and also in the visible absorption spectra in the presence of dithionite.