Ligands hemocyanin

Evidence tom a variety of sources indicates that the active site of tyrosinase is very similar to that of hemocyanin, a dioxygen-binding protein found in molluscs and arthropods (15,16). This type of active site contains two copper ions, which are cuprous in the deoxy state, and which reversibly bind dioxygen, forming the oxy form of the enzyme or protein in which a peroxy ligand bridges between two cupric ions. 

The veiy different reactivities of hemocyanin and tyrosinase toward oxidizable substrates se n to be due to the presence of a substrate binding site in the latter. It appears, therefore, that the oxygenation of the phenol substrate occurs either by reaction of copper-bound pooxide or hydrc ieroxide with the ortho position of the copper-bound phenol (16) or that the 0-0 bond of the peroxide ligand is cleaved... 

In a study of octopus hemocyanin (Salvato et al., 1989), a green half-methemocyanin could be formed in the presence of slight molar excess of sodium nitrite and ascorbate. This form was believed to consist of cuprous and cupric metals, but the amoung of NO directly bound was less than 0.1 mol. NOi was believed to be the oxidizing species its relationship to the endogenous ligand was not addressed. Apparently, hemocyanins are most likely to be found in deoxy, or reduced, forms, and it is difficult to oxidize them. 

As is the case for other copper-binding proteins, the ligands are further oriented by hydrogen bonding to neighboring atoms. There is a local twofold axis relating the Cu(A) and Cu(B) sites of hemocyanin ... 

Hemocyanin, 40 362-363 as cobalt complex ligands, 44 291 oxygen-carrying properties, 40 366 XAS, 36 326-327... 

A number of the above complexes may be alternatively considered as macrocyclic ligands or compartmental ligands, but as the emphasis has been primarily in terms of the local copper(I) stereochemistry and the polynuclear nature of the complexes, they have been included above. As there is no crystallographic data on biological copper(I) systems, this section will have to await the further refinement of the structure of Panutirus Interruptus hemocyanin.353... 

Figure 101 The absorption spectra of half-met-hemocyanin protein plus added bridging ligands 15 K IT —...

The binding of CO to hemocyanin is of interest. The two-coordinate copper centres in deoxyhemocyanin might each be expected to bind CO. However, some two-coordinate complexes of Cu1 with heterocyclic donor ligands show lack of reactivity towards CO in the absence of additional ligands, probably because the metal does not receive enough electron density to back bond to CO.1295... 

For the purpose of this calculation it was necessary to know the diffusion coefficient for ligand and whole molecules of hemocyanin (Table I) and the value of the diffusion coefficient for half molecules of hemocyanin. If the level of calcium ion is reduced in pH 9.6 glycine buffer to the point where no whole molecules remain, the half molecules always are contaminated with one-twelfth size (5S) subunits, so that it is impossible to measure directly the diffusion coefficient of half molecules. For a self-associating system, the Gouy method leads to an average diffusion coefficient which is the Z-average, defined by... 

Takano, Y., Yamaguchi, K., Hybrid density functional study of ligand coordination effects on the magnetic couplings and the Dioxygen binding of the models of hemocyanin. Int. J. Quantum Chem. 2007, 107, 3103-3119. 

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