The third subunit of desulfoviridin‐type dissimilatory sulfite reductases

Abstract

In addition to the 50‐kDa (α) and 40‐kDa (β) subunits, an 11‐kDa polypeptide has been discovered in highly purified Desulfovibrio vulgaris (Hildenborough) dissimilatory sulfite reductase. This is in contrast with the hitherto generally accepted α2β2 tetrameric subunit composition. Purification, high‐ionic‐strength gel‐filtration, native electrophoresis and isoelectric focussing do not result in dissociation of the 11‐kDa polypeptide from the complex. Densitometric scanning of SDS gels and denaturing gel‐filtration indicate a stoichiometric occurrence. A similar 11‐kDa polypeptide is present in the desulfoviridin of D. vulgaris oxamicus (Monticello), D. gigas and D. desulfuricans ATCC 27774. We attribute an α2β2γ2 subunit structure to desulfoviridin‐type sulfite reductases. N‐terminal sequences of the α, β and γ subunits are reported. Copyright © 1992, Wiley Blackwell. All rights reserved