Induced paramagnetism and hyperfine interactions in the {[Fe4S4]-Fe} active site of Escherichia coli sulfite reductase

✍ Scribed by Moisey I. Belinsky

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 639 KB
• Volume: 250
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(95)01456-x

✦ Synopsis

The spin-coupling model of the {[Fe4S4]-siroheme} center of the active site of sulfite reductase is developed. The tetmmer-siroheme coupling 2JthS j -s h results in the induced paramagnetism of individual ions of the Fe/S tetramer which = ~ __ 33/j

.j. provides non-zero effective hyperfine constants A1, 2 -A3, 4 yI. tJ )ai, where J is the parameter of the Heisenberg pair-pair interaction in the Fe/S tetramer and ai is the local hyperfine constant. The siroheme g-factor contributes dominantly to the molecular g-factor, the tetramer contribution is small (= (Jth/J) 2, Jth/J << 1). The model explains the observed paramagnetism of the Fe/S component of the active site in M/Sssbauer, ENDOR and I H NMR experiments and concurrently the diamagnetism of this moiety in magnetic and EPR measurements.

Sulfite reductase (SIR) catalyzes the six-electron reduction of SO~-to S 2-. The catalytically active center of the monomeric hemeprotein subunit (SIR-HP) of Escherichia coli sulfite reductase contains a