Oxygen hemocyanin

Figure 5.8 Wavefunction, Inc. Spartan 02 for Windows visualization of oxygenated hemocyanin from PDB data deposited as 1 OXY from reference 37a. See text for visualization details. Printed with permission of Wavefunction, Inc., Irvine, CA. (See color plate.)...

The copper pairs are 42 A apart within a dimer, so that the coopera-tivity exhibited by this protein clearly involves indirect interactions. The fact that partially oxygenated hemocyanin can be found in the same crystal form (albeit with higher concentrations of dimethyl sulfoxide, which is a denaturant) argues that the structural changes either are not large or are within the variability already exhibited by the fact that the crystals at present cannot diffract to better than 3.2 A. 

Figure 1. Depiction of active site structures and physical properties of deoxy (unoxygenated) and oxy (oxygenated) hemocyanin.

Figure 1. Effect of gamma irradiation on the oxygencarrying capacity of different concentrations of oxygenated hemocyanins in phosphate buffer at pH 7.0. The oxygenation reaction time was 10 minutes and the deoxygenation reaction time was 30 minutes...

Unlike mammals, snails, spiders, and octopuses do not use hemoglobin to transport oxygen. Instead, they rely on a related compound known as hemocyanin. This molecule doesn t have an atom of iron in its middle it has an atom of copper, which binds oxygen. Hemocyanin absorbs all colors except blue, which it reflects. 

In certain copper-containing proteins the copper appears to serve principally in electron transport with no evidence of CU-O2 interaction, such as in cytochrome oxidase. Of importance, however, is that many copper proteins and enzymes participate in reactions in which the oxygen molecule is directly or indirectly involved. An example is hemocyanin, the oxygen carrier in the blood of certain sea animals such as snails, octopus, and Crustacea. Oxygenated hemocyanin is blue and the cephalopods (crabs and lobsters) are literally the blue bloods of the animal kingdom. Hemocyanins are giant molecules of MW > 10 that occur free in solution. 

Copper is one of the twenty-seven elements known to be essential to humans (69—72) (see Mineral nutrients). The daily recommended requirement for humans is 2.5—5.0 mg (73). Copper is probably second only to iron as an oxidation catalyst and oxygen carrier in humans (74). It is present in many proteins, such as hemocyanin [9013-32-3] galactose oxidase [9028-79-9] ceruloplasmin [9031 -37-2] dopamine -hydroxylase, monoamine oxidase [9001-66-5] superoxide dismutase [9054-89-17, and phenolase (75,76). Copper aids in photosynthesis and other oxidative processes in plants. 

Senozan, N. et al. (1981) Hemocyanin of the giant keyhold limpet, Megathura crenulata. In Invertebrate Oxygen Binding Proteins Structure, Active Sites, andFunction (J. Lamy, and J. Lamy, eds.), pp. 703-717. Dekker, New York. 

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

Oxygenation rates were first examined for the system [Cu (R-XYL-H)]2+. In the model described here, two bis [2-(2-pyridyl)ethyl] amine (PY2) units are linked by a xylyl spacer group (R = H). Although initially proposed as a crude hemocyanin model, this system now is studied as a model for tyrosinase and is an example of hydrocarbon oxygenation taking place under mild conditions—that is, < 1 atm 02... 

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... 

Type III copper is characterized by antiferromagnetic coupling of a pair of copper atoms and strong absorbance at 330 nm. A single type III pair is found in hemocyanin, in which it is involved in O2 transport, and in tyrosinase, in which an oxygen is inserted into substrate. A pair of copper atoms is also found in the multi-copper ascorbate oxidase, but it is coupled to the type II copper in a trinuclear arrangement. 

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