Metalloproteins ligands

Lu, Y. Roe, J. A. Gralla, E. B. Valentine, J. S. Metalloprotein ligand redesign characterization of copper-cysteinate proteins derived from yeast copper-zinc superoxide dismutase. In Bioinorganic Chemistry of Copper Karlin, K. D. Tyeklar, Z., Eds. Chapman and Hall New York, 1993 pp 64-77. 

Sulfur-Containing Ligands in Metalloproteins and Enz mies (W. E. Newton)... 

TABLE 5 Ligand Preferences for Metals Commonly Found in Metalloproteins... 

Thiolates (RS ) represent an extensive family of ligands, and include chelating forms. Thiolates are known to act as monodentate donors, but often act in a bridging role. There is a clear biological interest, through participation of thiolates (cysteine residues) as donors in many metalloproteins both as terminal S donors and bridging ligands in, for example, Fe S clusters. 

Table 9 gives some cases where the rotational strengths of absorption bands have been measured in metalloproteins. At the present time these changes are not used to diagnose the nature of the ligands of the metal but rather they have been used to follow minor changes at the metal when substrates or inhibitors interact with the metals. The sensitivity of CD and MCD measurements to very small changes in the metal environment make them very attractive for protein/metal complex studies. 

This suggests that the g-strain in EPR spectra contains detailed geometric and energetic information on the 3-D position of ligand atoms for a given metalloprotein conformation with respect to a (virtual) cubic coordination, and therefore, of position and interconversion energy (by strain) of the 3-D position of ligand atoms in, say, two different protein conformations. This is an unexplored area of research. 

Zinc is the active metal in the largest group of metalloproteins found in the nature. Recently a new class of zinc enzymes with a sulfur-rich environment has emerged the thiolate-alkylating enzimes, the most prominent of which is the cobalamine-independent methionine synthase.126 For these reasons several monothiolate zinc complexes have been prepared for the modelling of these enzymes with different N2S as (13),127 130 N20,13° 132 N3,132,133 S3,134 tripod ligands, or with Cd because of the favourable spectroscopic properties with an S3 tripod ligand.135... 

The transfer of a quadridentate N2S2-donor ligand from M2+ (M = Cr, Mn, Fe, Co or Ni) to Cu2+ (271), already mentioned in Section V.A.l, has a formal connection with an investigation of the mechanism of copper delivery to metalloproteins, such as copper zinc superoxide dismutase. Both are ligand exchange reactions of the type ML + CuL ML + CuL (300). 

Here, we will first review the physical organic chemistry and spectroscopic features of the ligand phenoxyl and introduce briefly some well-characterized metalloproteins known to contain tyrosyl radicals and then systematically describe the coordination chemistry of uncoordinated and coordinated phenoxyls. Finally, we will describe the reactivity of coordinated phenoxyls toward some organic substrates. 

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