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Hemoglobin function in deep-sea and hydrothermal-vent endemic fish: Symenchelis parasitica (Anguillidae) and Thermarces cerberus (Zoarcidae)

Roy E. Weber^1,*, Stephane Hourdez², Francis Knowles³ and Francois Lallier⁴

¹ Department of Zoophysiology, C.F. Møllers Alle, Building 131, University of Aarhus, DK 8000 Aarhus C, Denmark
² Department of Biology, Pennsylvania State University, University Park, PA 16802, USA
³ Department of Chemistry, University of California at San Diego, La Jolla, CA 92093, USA
⁴ Station Biologique de Roscoff, UPMC-CNRS-INSU, 29682 Roscoff Cedex, France

View larger version (13K): [in a new window]   Fig. 1. Isoelectric focusing of erythrolysates of (A) Symenchelis parasitica and (B) Thermarces cerberus (described in Materials and methods). Circles, absorption at 540 nm; triangles, pH values at 22°C; solid rectangles, Hb-containing fractions that were pooled and dialysed for Hb–O2 binding studies; shaded rectangles, fractions that contained greyish precipitated material. I, II and III refer to hemoglobins (Hbs) I, II and III, respectively.

View larger version (22K): [in a new window]   Fig. 2. O2 equilibria of (A) Hb I and (B) Hb II of Symenchelis parasitica measured in 0.1 mol l-1 Hepes buffer at pH 7.2 in the absence of added anions (circles) and in the presence of either 0.1 mol l-1 Cl- (triangles) or 0.1 mol l-1 Cl- + saturating ATP concentration (ATP/tetrameric Hb ratio >100; diamonds), illustrating a large ATP effect and no Cl- effect on Hb I and distinct effects of both effectors on Hb II. Heme concentrations were 0.10 mmol l-1 (Hb I) and 0.05 mmol l-1 (Hb II). (7.50 Torr=1 kPa.)

View larger version (24K): [in a new window]   Fig. 3. P50 (O2 tension at half O2 saturation) and n50 (Hill cooperativity coefficient at P50) values of Symenchelis parasitica hemolysate (He, dotted line), Hb I (dashed lines) and Hb II (continuous lines) and their pH dependence in the absence of effectors and in the presence of 0.1 mol l-1 KCl, saturating ATP levels and peptide corresponding to the 10-mer amino-terminal segments of the cytoplasmic domain of Band 3 protein (cd-B3) from trout red cell membranes (peptide/Hb tetramer molar ratio=5) measured at 25°C (A) and 5°C (B). Other conditions are as described in the legend to Fig. 2. (7.50 Torr=1 kPa.)

View larger version (23K): [in a new window]   Fig. 4. Extended Hill plots (where Y is the fractional O2 saturation) of S. parasitica Hb at pH 7.04-7.06 and either 5°C (triangles) or 25°C (circles) and at pH 7.63 and 25°C (squares). The intercepts of the asymptotes to the lower parts of the curves (broken lines with slopes of unity) with the vertical axis at logPO indicate the KT (the O2 association constant of the low-affinity deoxy state of the molecules) values. Heme concentration, 0.80 mmol l-1. (7.50 Torr=1 kPa.)

View larger version (14K): [in a new window]   Fig. 5. P50 (O2 tension at half O2 saturation) values of (A) Thermarces cerberus Hbs I (circles), II (triangles) and III (inverted triangles) and (B) stripped Zoarces viviparus hemolysate, and their pH dependence at 15°C (semicircles), 25°C (stars) and 35°C (circles). Heme concentrations, 0.16 mmol l-1; Cl- concentration, 0.1 mol l-1. (7.50 Torr=1 kPa.)

View larger version (20K): [in a new window]   Fig. 6. (A) O2 equilibrium curves of Thermarces cerberus Hbs I, II and III in the absence of added anions (solid lines), the presence of 0.1 mol l-1 Cl- (dashed lines) and the presence of 0.1 mol l-1 Cl- and saturating ATP concentration (20-fold excess over Hb tetramers; dotted lines). (B) Bohr effect plots. Buffer, 0.1 mol l-1 Hepes; heme concentration, 0.16 mmol l-1. (7.50 Torr=1 kPa.)

View larger version (17K): [in a new window]   Fig. 7. van't Hoff plots of (A) Symenchelis parasitica Hbs I and II and (B) Thermarces cerberus Hbs I and II and Z. viviparus hemolysate. The data points at the indicated pH values were interpolated from logP50 vs pH curves at 5°C, 25°C and 35°C (Figs 3, 6) as described in Materials and methods. Numbers next to the lines are H (heat of oxygenation) values in kJ mol-1. (7.50 Torr=1 kPa.)

View larger version (35K): [in a new window]   Fig. 8. P50 (O2 tension at half O2 saturation) values of Thermarces cerberus (Therm) Hbs I and II and S. parasitica (Symen) Hbs I and II compared with those for Zoarces viviparus hemolysate (Zoarc), Hoplosternum littorale cathodic and anodic Hbs (Hoplo HbC and Hoplo HbA; Weber et al., 2000) and eel Anguilla anguilla cathodic HbC (Anguil HbC; Fago et al., 1995) at pH 7.0 and human Hb at pH 7.4 (Imai, 1982). Open columns, stripped Hbs; shaded columns, Hbs in the presence of 0.1 mol l-1 KCl; solid columns, Hbs in the presence of 0.1 mol l-1 KCl + saturating concentrations of ATP (fish Hbs) or 2,3-diphosphoglycerate (DPG; human Hb). Other conditions: 0.1 mol l-1 Hepes buffer (fish Hbs) or 0.05 mol l-1 Bis-Tris (Human Hb) and 25°C (20°C for Anguil HbC). (7.50 Torr=1 kPa.)