Search results for "hemocyanin"
showing 10 items of 148 documents
Allosteric Models for Multimeric Proteins: Oxygen-Linked Effector Binding in Hemocyanin
2005
In many crustaceans, changing concentrations of several low molecular weight compounds modulates hemocyanin oxygen binding, resulting in lower or higher oxygen affinities of the pigment. The nonphysiological effector caffeine and the physiological modulator urate, the latter accumulating in the hemolymph of the lobster Homarus vulgaris during hypoxia, increase hemocyanin oxygen affinity and decrease cooperativity of oxygen binding. To derive a model that describes the mechanism of allosteric interaction between hemocyanin and oxygen in the presence of urate or caffeine, studies of oxygen, urate, and caffeine binding to hemocyanin were performed. Exposure of lobster hemocyanin to various pH …
Small-angle X-ray scattering reveals differences between the quaternary structures of oxygenated and deoxygenated tarantula hemocyanin
1996
Small-angle X-ray scattering (SAXS) curves have been recorded for the oxygenated and deoxygenated states of the 4 x 6-meric hemocyanin from the tarantula Eurypelma californicum. A comparison of the curves shows that the quaternary structures of the two states are different by three criteria, which all indicate that the hemocyanin is less compact in the oxygenated compared to the deoxygenated form: (a) The radius of gyration is 8.65 +/- 0.05 nm for the deoxy- and 8.80 +/- 0.05 nm for the oxy-form. (b) The maximum particle dimension amounts to 25.0 +/- 0.5 nm for the deoxy- and to 27.0 +/- 0.5 nm for the oxy-form. (c) A dip in the intramolecular distance distribution function p(r) is more pro…
Structural properties, conformational stability and oxygen binding properties of Penaeus monodon hemocyanin
2004
Hemocyanin sequences allineament shows the presence of highly invariant regions especially in the active site and in the tight intersubunits interaction sites. Comparing the aminoacids in contact regions between monomers is possible to interpret the stability of hexamers.
Conversion of crustacean hemocyanin to catecholoxidase
2004
Crustacean hemocyanin as oxygen carrier and catecholoxidase as enzymes belong to the same protein family (type 3 copper proteins) sharing very similar active sites. Treatment with SDS of these hemocyanins results in an opening of the entrance to the active site for bulky phenolic compounds. This demonstrates, that almost all hemocyanin subunits possess the ability of catecholoxidase activity.
Red blood with blue-blood ancestry: Intriguing structure of a snail hemoglobin
2006
The phylogenetic enigma of snail hemoglobin, its isolated occurrence in a single gastropod family, the Planorbidae, and the lack of sequence data, stimulated the present study. We present here the complete cDNA and predicted amino acid sequence of two hemoglobin polypeptides from the planorbid Biomphalaria glabrata (intermediate host snail for the human parasite Schistosoma mansoni ). Both isoforms contain 13 different, cysteine-free globin domains, plus a small N-terminal nonglobin “plug” domain with three cysteines for subunit dimerization (total M r ≈ 238 kDa). We also identified the native hemoglobin molecule and present here a preliminary 3D reconstruction from electron microscopical …
Molecular cloning and evolution of lobster hemocyanin.
2001
In the American lobster, Homarus americanus, oxygen is transported by a hemocyanin that is composed 2 x 6 subunits. N-terminal sequencing show the presence of three distinct subunit types (alpha, beta and gamma). We cloned the cDNA of one of these subunits that belong to the alpha-type. It encodes a hemocyanin subunit of 654 amino acids with a molecular mass of 84.8 kDa, which is synthesized in the hepatopancreas. Phylogenetic analyses of the crustacean hemocyanin sequences show two well-separated clades, which correspond to the alpha and gamma-type subunits. Sequences of beta-type subunits are still unknown. The gamma-sequences have evolved about 15% faster than the alpha-subunits, consist…
Bohr-effect and buffering capacity of hemocyanin from the tarantula E. californicum.
2003
A previous report showed that binding of oxygen to the 24-meric hemocyanin from E. californicum does not correlate linearly with the release of protons as known from hemoglobin. However, this unusual complex phenomenological observation could not be explained at that time. Here, I present a full analysis of the thermodynamic coupling between protons and oxygen for the 24-meric tarantula hemocyanin in Ringer-solution based on the Nested-MWC-model. A strategy is presented which allows to reduce the number of free parameters when fitting the model to the data by including explicitly the equilibrium constants for binding of protons to the different conformations. The results show that the Neste…
Toward oxygen binding curves of single respiratory proteins
2004
Oxygen binding curves of single molecules promise to discriminate between different models describing cooperativity because load distributions are accessible. Individual tarantula hemocyanins could be detected by fluorescence correlation spectroscopy using intrinsic tryptophan fluorescence as sensor of bound oxygen. However, imaging of immobilized proteins was not possible due to fast photo-bleaching. It is shown that tetra-methyl-carboxy-rhodamine (TAMRA), commonly used as a fluorescence label in single-molecule spectroscopy, can also be applied to monitor bound oxygen. The dye's fluorescence is quenched due to Förster energy transfer to the oxygenated active sites of hemocyanin.
Diplopod hemocyanin sequence and the phylogenetic position of the Myriapoda
2001
Hemocyanins are copper-containing respiratory proteins of the Arthropoda that have so far been thoroughly investigated only in the Chelicerata and the Crustacea but have remained unstudied until now in the Myriapoda. Here we report the first sequence of a myriapod hemocyanin. The hemocyanin of Spirostreptus sp. (Diplopoda: Spirostreptidae) is composed of two distinct subunits that are arranged in a 6 x 6 native molecule. The cloned hemocyanin subunit cDNA codes of for a polypeptide of 653 amino acids (75.5 kDa) that includes a signal peptide of 18 amino acids. The sequence closely resembles that of the chelicerate hemocyanins. Molecular phylogenetic analyses reject with high statistical con…
Subunit sequences of the 4 x 6-mer hemocyanin from the golden orb-web spider, Nephila inaurata. Intramolecular evolution of the chelicerate hemocyani…
2003
The transport of oxygen in the hemolymph of many arthropod and mollusc species is mediated by large copper-proteins that are referred to as hemocyanins. Arthropod hemocyanins are composed of hexamers and oligomers of hexamers. Arachnid hemocyanins usually form 4 x 6-mers consisting of seven distinct subunit types (termed a-g), although in some spider taxa deviations from this standard scheme have been observed. Applying immunological and electrophoretic methods, six distinct hemocyanin subunits were identified in the red-legged golden orb-web spider Nephila inaurata madagascariensis (Araneae: Tetragnathidae). The complete cDNA sequences of six subunits were obtained that corresponded to a-,…