PMID:6281269
| Citation |
Siegel, LM, Rueger, DC, Barber, MJ, Krueger, RJ, Orme-Johnson, NR and Orme-Johnson, WH (1982) Escherichia coli sulfite reductase hemoprotein subunit. Prosthetic groups, catalytic parameters, and ligand complexes. J. Biol. Chem. 257:6343-50 |
|---|---|
| Abstract |
Escherichia coli NADPH-sulfite reductase can be dissociated into an oligomeric flavoprotein and a monomeric hemoprotein (HP) subunit in 4 M urea. HP catalyzes stoichiometric 6-electron reductions of SO32- (to S2-) and of NO2-, as well as 2-electron reduction of NH2OH, with reduced methyl viologen (MV+) as reductant. While Vmax values are highest with the nitrogenous substrates, Km for SO32- is 2 to 3 orders of magnitude less than the Km for NO2- or NH2OH. EPR spectroscopic and chemical analyses show that HP contains one siroheme and one Fe4S4 center per polypeptide. The heme is in the high spin Fe3+ state in HP as isolated. Near-quantitative reduction of the Fe4S4 center to a state yielding a g = 1.94 type of EPR spectrum by S2O42- and/or MV+ could be achieved if HP was converted to either the CN- or CO complex or treated with 80% dimethyl sulfoxide. HP binds one SO32- or CN- per peptide. Binding of these ligands, as well as CO, appears to be mutually exclusive and to involve the heme. The heme Fe3+/Fe2+ potential is shifted from -340 mV in the free HP to -155 mV in the HP-CN- complex. The potential of the Fe4S4 center is approximately 70 mV more negative in the CN- as opposed to the CO-ligated HP (-420 mV), a result which indicates the presence of heme-Fe4S4-ligand interaction in the HP complexes. |
| Links | |
| Keywords |
Cyanides/pharmacology; Electron Spin Resonance Spectroscopy; Escherichia coli/enzymology; Hemeproteins/isolation & purification; Hemeproteins/metabolism; Kinetics; Ligands; Oxidoreductases/metabolism; Oxidoreductases Acting on Sulfur Group Donors/isolation & purification; Oxidoreductases Acting on Sulfur Group Donors/metabolism; Protein Binding |
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