tailieunhanh - Báo cáo khoa học: Oxygen binding and its allosteric control in hemoglobin of the primitive branchiopod crustacean Triops cancriformis

Branchiopod crustaceans are endowed with extracellular, high-molecular-mass hemoglobins (Hbs), the functional and allosteric properties of which have largely remained obscure. The Hb of the phylogenetically ancientTri-ops cancriformis(Notostraca) revealed moderate oxygen affinity, coopera-tivity and pH dependence (Bohr effect) coefficients: P50¼ mmHg, n50¼, andu¼), at 20 C and pH in Tris buffer. Thein vivo hemolymph pH was . | ễFEBS Journal Oxygen binding and its allosteric control in hemoglobin of the primitive branchiopod crustacean Triops cancriformis Ralph Pirow1 Nadja Hellmann2 and Roy E. Weber3 1 Institute of Zoophysiology University of Munster Germany 2 Institute of Molecular Biophysics Johannes Gutenberg University of Mainz Germany 3 Zoophysiology Institute of BiologicalSciences University of Aarhus Denmark Keywords allosteric control Crustacea hemoglobin oxygen binding Correspondence R. Pirow Institute of Zoophysiology Hindenburgplatz 55 University of Munster D-48143 Munster Germany Fax 49 251 8323876 Tel 49 251 8323858 E-mail pirow@ Received 19 January 2007 revised 13 April 2007 accepted 8 May 2007 doi Branchiopod crustaceans are endowed with extracellular high-molecular-mass hemoglobins Hbs the functional and allosteric properties of which have largely remained obscure. The Hb of the phylogenetically ancient Triops cancriformis Notostraca revealed moderate oxygen affinity cooperativity and pH dependence Bohr effect coefficients P50 mmHg n50 and u at 20 C and pH in Tris buffer. The in vivo hemolymph pH was . Bivalent cations increased oxygen affinity Mg2 exerting a greater effect than Ca2 . Analysis of cooperative oxygen binding in terms of the nested Monod-Wyman-Changeux MWC model revealed an allosteric unit of four oxygen-binding sites and functional coupling of two to three allosteric units. The predicted 2 X 4 and 3 X 4 nested structures are in accord with stoichiometric models of the quarternary structure. The allosteric control mechanism of protons comprises a left shift of the upper asymptote of extended Hill plots which is ascribable to the displacement of the equilibrium between at least two high-affinity relaxed states similar to that found in extracellular annelid and pulmonate molluscan Hbs. Remarkably Mg2 ions increased oxygen affinity solely by displacing the equilibrium between the tense and

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