Mollusc hemocyanin

Activation mechanism. What happens during activation in hemocyanins and how can we use them as model systems to understand tyrosinase/catecholoxidase activity Arthropod and mollusc hemocyanins have to be considered separately, although the processes are similar. 

A similar substrate-binding pocket was identified for molluscan hemocyanins, which was not surprising since the active site of mollusc hemocyanins and that of arthropod hemocyanins and catecholoxidases are very similar. Therefore, we proposed the following mechanism for the activation of the molluscan hemocyanin based on the recently solved X-ray structure of a fimctional unit of the hemocyanin from the molluscan O. dofleini The C-terminal domain covers the entrance to the active site located on the N-terminal site by sticking Leu2830 into the entrance door. Detergents... 

Synthesis and conformational analysis of xylose-containing elements of mollusc hemocyanin glycans... 

In the framework of the primary structural analysis and the biosynthesis of mollusc hemocyanin glycans, attention has also been paid to the organic synthesis of structural... 

The active site of type 3 copper proteins consists of two copper atoms. Each of them is bound by three histidines provided by an antiparallel alpha-helix pair (Figure 1). Cu-A denotes the copper-binding site closer to the N-terminus, whereas Cu-B is the copper-binding site closer to the C-terminus. According to crystal structures of arthropod and mollusc hemocyanins, the coppers bind a dioxygen molecule in the same way as a peroxide in side-on... 

In the molluscs hemocyanin is found in cephalopods and gastropods (prosobranchs and pulmonates). Recently it was also identified in a species of amphineura Cryptochiton stelleri (Steward et al., 1952). Hemocyanin is not found in the lamellibranchs (Woods, et al., 1958) many species of opisthobranchs, tectibranchs (Aplysia, Bulla, Tethis, Navanax), and also some species of nudibranchs do not possess it (Ghiretti et al., 1959, Manwell, 1960b). 

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... 

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. 

Like hemerythrin, hemocyanin is an oxygen transport non-heme-containing protein found in some arthropods and molluscs (104,105). In the 02-bound form, hemocyanin contains an antiferromagnetically coupled binuclear copper(II) system (106) ligated by histidine residues, with a sideways / 2-v2 V2 peroxo group bound to both Cu11 centers (104), which superseded the previous model (107). 

Occurrence of hemocyanin related proteins in organisms. While textbooks teU that Hes occm only in arthropods and molluscs, recently Hes were also found in other phyla. The velvet worms (Onychophora) are considered living fossils and are closely related to the Euarthropoda. Onychophora possess a tracheal system for respiratory function, thus oxygen transport proteins have been considered unnecessary. In the hemolymph of the Epiperipatus sp. (Onychophora Peripatidae), an arthropod-type hemocyanin was found, demonstrating that such proteins exist outside the Euarthropoda. ... 

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