Nature of Labile Sulfur

Models of the Iron Coordination Structure A. Chemical Nature of Labile Sulfur 

An intriguing chemical feature of non-heme iron proteins of the ferredoxin group is the so-called labile sulfur . There is some contradiction in interpretations of the chemical nature of this unusual sulfur . 

and Kazmaier (7) proposed that labile sulfur originates from cysteinyl residues by a p-elimination reaction in the presence of 

Therefore, the hairpin-type linear arrangement of iron atoms bridged with sulfur atoms, proposed independently by Blomstrom et al. (10), Tanaka et al. (64), and Brinzinger et al. (11) is generally favored. 

The third structure of labile sulfur is a persulfide linkage which has been proposed by Massey and his coworkers (39) for dihydroorotate dehydrogenase. This enzyme has 2 atoms of iron, and 2 moles of labile sulfur besides its flavin moiety. They suggested that in catalysis the iron sulfide functions as an iron-sulfur radical, and the iron is not reduced by substrate. 

---