Journal of Biochemistry Advance Access published online on November 4, 2007
Journal of Biochemistry, doi:10.1093/jb/mvm210
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© 2007 The Japanese Biochemical Society
Structural and functional characterization of hemocyanin from the anemone hermit crab Dardanus calidus
1Dipartimento di Scienze Applicate ai Biosistemi, Università di Cagliari, Cittadella Universitaria, I-09042 Monserrato (CA) Italy
2Istituto di Biochimica e Biochimica Clinica, Facoltà di Medicina, Università Cattolica, Largo F. Vito 1, I-00168 Roma, Italy
3Istituto per la Chimica del Riconoscimento Molecolare, CNR, Largo F. Vito 1, I-00168 Roma, Italy
4Dipartimento di Biologia Animale ed Ecologia, viale Poetto 1, I-09126, Cagliari, Italy
*Corresponding author: Prof. Maria Teresa Sanna, Dipartimento di Scienze Applicate ai Biosistemi, Università di Cagliari, Cittadella Universitaria, I-09042 Monserrato (CA) Italy; Telephone number: +39 070 6754509; Telefax number: +39 070 6754523, E-mail address: sanna{at}unica.it
Received August 8, 2007; Accepted October 27, 2007
| Abstract |
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Oxygen-binding to hemocyanin (Hc) is generally an exothermic process, with overall enthalphy of oxygenation varying from species to species. A number of crustacean Hcs showed a null or reduced enthalphy of oxygenation, among others, the anomuran Pagurus bernhardus and Paralithodes camtscaticae possess a completely temperature-independent oxygen-binding in a wide range of temperature and pH. Functional analysis performed on purified native, hexameric and dodecameric Hc forms of the anemone hermit crab Dardanus calidus allowed to calculate the enthalphy of oxygenation values that resulted equal to –36.2 kJ/mol, –33.8 kJ/mol and –26.8 kJ/mol, respectively. Thus, the temperature sensitivity of oxygen-binding of D. calidus Hc is in contrast with the temperature independence reported for P. bernhardus and P. camtscaticae, suggesting a high Hc functional heterogeneity within Anomura. Functional characterization also evidenced a strong oxygen affinity modulation by protons (
logP50/
pH = –0.97) and lactate (
logP50/
log[lactate] = –0.38), and a significant decrease in cooperativity by physiological concentration of lactate (n50 from 2.8 to 1.7 at pH 7.5).
Key Words: Bohr effect, enthalphy of oxygenation, lactate binding, oxygen affinity, subunit heterogeneity
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