Abstract
We have studied a low-molecular-weight (Mr = 27,200) sulfite reductase from Desulfovibrio vulgaris (Hildenborough, NCIB 8303) with Mössbauer, EPR, and chemical techniques. This sulfite reductase was found to contain one siroheme and one [4Fe-4S] cluster. As purified, the siroheme is low-spin ferric (S = 1/2) which exhibits characteristic EPR resonances at g = 2.44, 2.36, and 1.77. At 150 K, the observed Mössbauer parameters, delta EQ = 2.49 +/- 0.02 mm/s and delta = 0.31 +/- 0.02 mm/s, for the siroheme are typical for low-spin ferric complexes. The [4Fe-4S] cluster is in the 2+ state. The Mössbauer parameters, delta EQ = 0.95 +/- 0.02 mm/s and delta = 0.38 +/- 0.02 mm/s, for the cluster are almost identical to those observed for the [4Fe-4S]2+ cluster in the hemoprotein subunit of the sulfite reductase from Escherichia coli. Similar to the hemoprotein subunit of E. coli sulfite reductase, low-temperature Mössbauer spectra of D. vulgaris sulfite reductase recorded with weak and strong applied fields also show evidence for an exchange-coupled siroheme-[4Fe-4S] unit.
Highlights
From the $Departmentof Physics, Emory University, Atlanta,Georgia 30322 and the $Departmentof Biochemistry, Uniuersity of Georgia, Athens, Georgia 30602
The assimilatory-type sulfite reductase consists of cluster in the hemoprotein subunitof the sulfite a single polypeptide chain and has asmaller molecular weight reductase from Escherichia coli
It is capable of reducing protein subunit of E. coli sulfite reductase, low-tem- sulfite in the presence of reduced methyl viologen, and the perature Mossbauer spectraof D. vulgaris sulfite re- sole product of the reduction is sulfide
Summary
EVIDENCE FOR THE PRESENCE OFALOW-SPIN SIROHEME ANDAN EXCHANGE-COUPLED SIROHEME-[4Fe-4S] UNIT*. Coli NADPH-sulfite reductase disclosedthat thesiroheme and the [4Fe-4S] clusters are exchange-coupled [13,14,15]. Its optical spectrum exhibits maxima at 628,580,408,390, and 279 nm, and its reaction mechanism is typical for dissimilatory sulfite reductase. The assimilatory-type sulfite reductase consists of cluster in the hemoprotein subunitof the sulfite a single polypeptide chain and has asmaller molecular weight reductase from Escherichia coli. Similar to the hemo- (a value of26,800was reported) It is capable of reducing protein subunit of E. coli sulfite reductase, low-tem- sulfite in the presence of reduced methyl viologen, and the perature Mossbauer spectraof D. vulgaris sulfite re- sole product of the reduction is sulfide. We report asimple procedure for purifying the low-molecularweight sulfite reductase from D. vulgaris. Assimilatory sulfite reductases which are involved in the synthesis of sulfur-containing cell constituents, and 2) dissimi-
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