Hemocyanin cooperativity

Ross, P. K., and E. I. Solomon. 1991. An Electronic Structural Comparison of Cooper-Peroxide Complexes of Relevance to Hemocyanin and Tyrosinase Active Sites. J. Am. Chem. Soc. 113, 3246. 

The deoxy forms of hemocyanins are colorless, as a result of their 3d ° dicopper(I) centers. Although chemical and x-ray absorption spectroscopic studies had shed considerable light on the nature of the deoxy-He dicopper binding site, there now exist two x-ray crystal structures, the first on the the spiny lobster He, Panulirus interruptus [23], and a recent one of the horseshoe crab Limulus II protein [24], The structures exhibit rather different active-site characteristics, and since the former was crystallized at low pH and possesses rather odd copper coordination, the latter Limulus II structure is probably representative. It indicates that the two Cu(I) ions are 4.6 A apart, each found in a trigonal-planar coordination environment with Cu-NMs bond distances of about 2.0 A (Figure 1). Intersubunit 02 binding cooperative effects are probably initiated and trans-... 

The function of domain 1 has not yet been completely elucidated, although it may function as a medium of cooperative oxygen binding [37]. Domain 3 screens the copper center of domain 2 [237] from solvent. This copper center in domain 2 [34] is coordinated by six histidines from the helices 2.1 (2 His), 2.5 (2 His), 2.2 (1 His), and 2.6 (1 His). The histidine residue of helix 2.1 occurs in the sequence His-His-Trp-His-Trp-His, which is conserved in many arthropod hemocyanins. The histidines in helix 2.5 occur in the structure His-X-X-X-His. The coordination of two copper atoms with six ligands leaves two coordination sites free these two sites are utilized to bind oxygen [34],... 

Brouwer M, Bonaventura C, Bonaventura J (1982) Chloride and pH dependence of cooperative interactions in Limulus polyphemus hemocyanin. In Bonaventura J, Bonaventura C, Tesh S (eds) Physiology and biology of horseshoe crabs studies on normal and environmentally stressed animals. Alan R Liss, New York, p 231... 

Figure 3 Hierarchies in the structures of hemocyanins from arthropods and molluscs. A kidney shaped arthropod subunit (Mr 72 kDa) binds one molecule of dioxygen. Depending on the species, the subunits associate to 1 x 6, 2 x 6, 4 x 6, 6 x 6 and 8 X 6-meric hemocyanins found freely dissolved in the hemolymph. A molluscan hemocyanin subunit (Mr 400 kDa) folds into eight functional units each carrying one active site (two cannot be seen being hidden in the interior of the cylinder). Ten of these subunits form cylinders. Depending on the species, decamers or didecamers are found. Thus, hemocyanins can bind up to 160 dioxygen molecules with a cooperativity h of over 11...

Similar to Hb. hemocyanins demonstrate a high degree of cooperativity in oxygen binding. Chemical and spectroscopic similarities of the mollusc and arthropod forms indicate a closely related active site stmeture and binding mode. Oxygenation of the dinuclear center alters... 

X 10 s 38 = 1.8 X 10 s. Even in the absence of cooperative phenomena, 08 binding by hemocyanin involves a minimum of two elementary steps, and this finding might be correlated with the presence of two metal atoms in each site. Raman spectroscopy has been used to investigate the nature of the co-ordination of iron in clostridial rubredoxin, and e.s.r. and Mossbauer spectroscopy have been used to study the non-haem iron proteins cysteamine oxygenase and adrenodoxin. ... 

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