Copper biologic sites

The low-temperature MCD and absorption titration studies (Figure 10) have determined that azide binds to both the type 2 and type 3 centers with similar binding constants. A series of chemical perturbations and stoichiometry studies have shown that these effects are associated with the same azide. This demonstrates that one N3 bridges between the type 2 and type 3 centers in laccase. These and other results from MCD spectroscopy first defined the presence of a trinuclear copper cluster active site in biology (89). At higher azide concentration, a second azide binds to the trinuclear site in laccase. Messerschmidt et al. have determined from X-ray crystallography that a trinuclear copper cluster site is also present in ascorbate oxidase (87, 92) and have obtained a crystal structure for a two-azide-bound derivative (87). It appears that some differences exist between the two-azide-bound laccase and ascorbate oxidase derivatives, and it will be important to spectroscopically correlate between these sites. 

Whittaker, J. W., 1994, The free radical-coupled copper active site in galactose oxidase. Metal Ions in Biology, Editors Sigel, H. and Sigel, A., Marcel Dekker publishers, 30 3159 360. 

The majority of cyanide-bridged dinuclear complexes described for the combination of metal ions belong to the biologically relevant class of Cu —Fe dimers. These compounds serve as models for the binuclear cyanide-inhibited site of cytochrome c oxidase, an enzyme that contains the heme-copper active site responsible for the O2 reduction chemistry (59). The lethal toxicity of cyanide was traced to its irreversible binding and inhibition of this active site in the enzyme (60). The biologically relevant aspects of these complexes were the subject of many reports (61,62). Our interest is in describing their crystal structure, which will be correlated to the magnetic properties in a later section. 

R. S. Czemuszewicz, G. Fraczkiewicz, R. Fraczkiewicz, B. C. Dave, and J. P. Germanas, Ground and Excited State Dynamics of Blue Copper Active Site from Resonance Raman Spectroscopy of Azurin, in Spectroscopy of Biological Molecules , eds. J. C. Merhn, S. Turrel, and J. P. Huvenne, Kluwer Academic Puhhshers, Dordrecht, The Netherlands,... 

Apparently nature has for ever utilized heteropolymetallic sites to realize some biological processes. The copper-iron site in cytochrome oxidase and the copper-zinc site in superoxide dismutase are two well known examples of this. Maybe nature has chosen heteropolymetallic sites when the effect desired was so subtle that no homometallic site could achieve it. 

Table 1. EPR Parameters of the Representative Copper Active Sites in Biology...

As listed in Table 1, biological copper active sites have been classified by their unique spectral features relative to those of the normal Cu(II) complexes, which typically have tetragonal ligand field environments [4,5], Classically, these have been divided into type 1 (Tl), type 2 (T2), and type 3 (T3) sites [6]. The T2 or normal copper sites exhibit spectral features similar to those of small-molecule inorganic Cu(II) complexes. The T2 site exhibits an electron paramagnetic reso-... 

Amino acid is one of the most important biological ligands. Researches on the coordination of metal-amino acid complexes will help us better understand the complicated behavior of the active site in a metal enzyme. Up to now many Ln-amino acid complexes [50] and 1 1 or 1 2 transition metal-amino acid complexes [51] with the structural motifs of mononuclear entity or chain have been synthesized. Recently, a series of polynuclear lanthanide clusters with amino acid as a ligand were reported (most of them display a Ln404-cubane structural motif) [52]. It is also well known that amino acids are useful ligands for the construction of polynuclear copper clusters [53-56], Several studies on polynuclear transition metal clusters with amino acids as ligands, such as [C03] [57,58], [Co2Pt2] [59], [Zn6] [60], and [Fe ] [61] were also reported. 

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