Hemocyanin dioxygen transport

Oxygen transport (binuclear) Hemocyanin Mollusks and arthropods Dioxygen transport... 

Copper, Cu ((f ) 5, square pyramid 6, tetragonal O-Carboxylate, A-imidazoIe Type II copper oxidases, hydoxylases Type III copper hydroxylases, dioxygen transport in hemocyanin... 

Cobalt Inorganic Coordination Chentistry Copper Hemocyanin/Tyrosinase Models Copper Inorganic Coordination Chemistry Copper Proteins Oxidases Copper Proteins with Dinuclear Active Sites Iron Heme Proteins Dioxygen Transport Storage Iron Heme Proteins, Mono- Dioxygenases Iron Models of Proteins with Dinuclear... 

As noted earlier, three solutions to the problem of dioxygen transport have evolved hemoglobin (Hb), hemocyanin (He), and hemerythrin (Hr). Their remarkable distribution over plant and animal kingdoms is shown in Figure 4.8.The hemoglobins and myoglobins found in plants, snails, and vertebrates all appear to share a common, very ancient ancestor. There is some evidence now for a common ancestral hemocyanin.The appearance of hemerythrin in a few annelid worms is an evolutionary curiosity. These few words and the diagram will... 

Hemocyanins are large, multisubunit dioxygen transporting proteins found in the hemolymph of many invertebrate species of the phyla of molluscs and arthropods 14). The subunits of molluscan hemocyanins contain functional units with a molecular weight of about 50,000 Da, each of which contains a dioxygen binding dicopper center. Arthropodal hemocyanins occur as hexamers, or multihexamers of subunits with a molecular weight of about 75,000 Da. As shown by the comparison of various X-ray crystal structures of the proteins from Panulirus interruptus (IS), Limulus polyphemus... 

Our biomimetic investigations have focused on the metalloproteins hemocyanin (He) (11-17) and tyrosinase (11,12,14,16,18,29), which contain two copper ions in their active center. The function of hemocyanin is to bind and transport dioxygen in the hemolymph of molluscs and arthropods. Studies employing EXAFS spectroscopy have shown that in the deoxy form, two (19-21) or three (13,21) imidazole units fiom protein histidine residues coordinate to each cuprous ion. Upon addition of O2 to give oxy-Hc, considerable changes take place in the coordination sphere giving rise to tetragonally coordinated Cu(II) ions... 

Hemocyanin [30,31], tyrosinase [32] and catechol oxidase (2) [33] comprise this class of proteins. Their active sites are very similar and contain a dicopper core in which both Cu ions are ligated by three N-bound histidine residues. All three proteins are capable of binding dioxygen reversibly at ambient conditions. However, whereas hemocyanin is responsible for O2 transport in certain mollusks and arthropods, catechol oxidase and tyrosinase are enzymes that have vital catalytic functions in a variety of natural systems, namely the oxidation of phenolic substrates to catechols (Scheme 1) (tyrosinase) and the oxidation of catechols to o-quinones (tyrosinase and catechol oxidase). Antiferromagnetic coupling of the two Cu ions in the oxy state of these metalloproteins leads to ESR-silent behavior. Structural insight from X-ray crystallography is now available for all three enzymes, but details... 

Copper has an essential role in a number of enzymes, notably those involved in the catalysis of electron transfer and in the transport of dioxygen and the catalysis of its reactions. The latter topic is discussed in Section 62.1.12. Hemocyanin, the copper-containing dioxygen carrier, is considered in Section 62.1.12.3.8, while the important role of copper in oxidases is exemplified in cytochrome oxidase, the terminal member of the mitochondrial electron-transfer chain (62.1.12.4), the multicopper blue oxidases such as laccase, ascorbate oxidase and ceruloplasmin (62.1.12.6) and the non-blue oxidases (62.12.7). Copper is also involved in the Cu/Zn-superoxide dismutases (62.1.12.8.1) and a number of hydroxylases, such as tyrosinase (62.1.12.11.2) and dopamine-jS-hydroxylase (62.1.12.11.3). Tyrosinase and hemocyanin have similar binuclear copper centres. 

The VBCI model has been employed for the interpretation of the optical absorption and CD spectra of of peroxo bridged Cu dimers like oxy-Hemocyanin and corresponding small-molecule analogs (Figure 3).i "i 44-26 Hemocyanin (He), the oxygen-transport protein of mollusks and arthropods, contains a binuclear Cu(I) active site that reversibly binds dioxygen as peroxide in a... 

Most of the synthetic models we found in our literature survey are concerned with hemocyanine, the oxygen transport protein in arthropods and molluscs, and tyrosinase, which catalyzes the two-electron oxidation of phenolic compounds. Both proteins contain a coupled binuclear copper active site, a Type III copper centre,"which reversibly binds dioxygen as peroxide bridging between the two copper ions" [153]. The Cu-Cu distance is of the order of 300-400 pm, and a tetragonal coordination is achieved with donor nitrogen atoms of imidazole ligands from histidine [142]. 

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