Plant sulfite reductase: molecular structure, catalytic function and interaction with ferredoxin

Plant sulfite reductase contains the siroheme and the [4Fe-4S] cluster as c atalytically active redox centers and catalyzes the six-electron reductions of sulfite and nitrite using electrons donated from ferredoxin. A heterolo gous expression of a cDNA for maize sulfite reductase in E. coli has enable d us to produce the wild-type and mutant enzymes. Putative substrate-bindin g basic residues, located at the siroheme distal side, have been substitute d for other residues with neutral or negatively charged side chains. Kineti c studies of the resulting mutant enzymes have demonstrated that substrate specificity for the two anions is remarkably changed by amino acid substitu tions at a single site. We have also produced two classes of ferredoxin mut ants with less ability to donate electrons to sulfite reductase: one with a defect in the recognition of the partner enzyme and the other with an unfa vorable redox property. This article summarizes our knowledge about the str ucture function relationships of plant sulfite reductase. (C) 2000 Elsevier Science B.V. All rights reserved.