FejSj clusters

In the first family, the metal is coordinated by one molecule of the pterin cofactor, while in the second, it is coordinated to two pterin molecules (both in the guanine dinucleotide form, with the two dinucleotides extending from the active site in opposite directions). Some enzymes also contain FejSj clusters (one or more), which do not seem to be directly linked to the Mo centers. The molybdenum hydroxylases invariably possess redox-active sites in addition to the molybdenum center and are found with two basic types of polypeptide architecture. The enzymes metabolizing quinoline-related compounds, and derivatives of nicotinic acid form a separate groups, in which each of the redox active centers are found in separate subunits. Those enzymes possessing flavin subunits are organized as a2jS2A2, with a pair of 2Fe-2S centers in the (3 subunit, the flavin in the (3 subunit, and the molybdenum in the y subunit. 

The enzyme, CobG, central to the foregoing research, is a fascinating iron-sulfur protein with a brown-green colour. Its content of iron and sulfur points to one [Fe4S4] or two [FejSj] clusters being present [110] and no cofactors besides oxygen need be added for full activity. 

R.E. Duderstadt, et al.. Effects of mutations in aspartate 14 on the spectroscopic properties of the [FejSJ" clusters in Pyrococcus furiosus ferredoxin. Biochemistry 1999, 38, 10585-10593. 

The iron EXAFS data are suggested to be consistent with but not restricted to a structure for the cofactor of either two FejSj units bridged by a molybdenum atom, or as in the MoFe7Se core found for the cluster [L3MoFe7S6(SR)7] , which involves a cube of metal ions with quadruply bridging sulfurs occupying the six faces of the cube. However, this stoichiometry is inconsistent with recent analytical data, and with Fe ENDOR measurements on the MoFe protein, which... 

Iron and sulfur can be extracted from F. the resulting apoferredoxin is reactivated by iron(II) salts and sulfides. The synthesis of the iron-free protein has been achieved by the Merrifield technique. On account of their properties as redox systems (Fe +e" Fe ") the F. effect electron transport between enzyme systems but do not exhibit any enzymatic activity. They transport electrons in the respiratory chain, in photosynthesis, and in nitrogen fixation. The iron-sulfur protein P439 of the Fc4S4-type (Mr 11600) plays a role in photosynthesis. Conclusions can be drawn about the evolutionary histories of plants from the similarities and differences in the amino acid sequences. For the evolutionary history of F. in photosynthesis, see Lit.K F. with FejSj- and FejSg-clusters also occur in bacteria Lit. TrendsBiochem.Sci. 13,30-33(1988). FEMSMicrobiol. Rev. 54,155-176 (1988) Trends Biochem. Sci. 13,369 f. (1988). 

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