maenas (intertidal zone) and Segonzacia mesatlantica - Station ...
maenas (intertidal zone) and Segonzacia mesatlantica - Station ... maenas (intertidal zone) and Segonzacia mesatlantica - Station ...
200 CHAPITRE 5. ADAPTATIONS RESPIRATOIRES DE S. MESATLANTICA FIG. 5.12 – Biplot graph of the canonical redundancy analysis (RDA) of the hemolymph composition effect on complex proportions along the two first canonical axis. Dotted arrows, explanatory variables ; full lines, response variables. to L-lactate. Lactate curves were calculated with the assumption that lactate did not modify the Bohr effect, even if lactate can alter the Bohr effect in some species. A second order polynomial was used to fit P 50 values vs pH without lactate (log(P 50 ) = 0.9088pH 2 − 15.781pH + 67.625, r2=0.9847) and the second and first order coefficients were kept for fitting with the data points with lactate, resulting in a change in the third constant only. From these curves a L-lactate effect was calculated ( ∆log(P 50) ∆log[lactate] ) and had a value of -0.276 and -0.174 in another experiment (average = 0.225), compared to -0.095 for C. maenas (Figure 5.13). The cooperativity of S. mesatlantica Hc is quite low (1.28-2.58), which could be due to the freezing and storage at -80°C (Morris, 1988). When the urate effect was studied, no effect could be observed up to 333 µM urate (Figure 5.14). The Bohr effect was not affected either. This is in contrast with the data for C. maenas ( ∆log(P 50) ∆log[urate] =- 0.22, (Lallier et Truchot, 1989)). The magnesium effect was tested simultaneously on S. mesatlantica and C. maenas Hc. For both species, affinity increased with increasing concentrations of Mg 2+ ; however the magnesium effect was more pronounced for S. mesatlantica than for C. maenas ( ∆log(P 50) =-0.24 vs -0.14, respectively) (Figure 5.15). It was also clear during these experiments that C. maenas Hc had a much ∆log[Mg 2+ ] higher cooperativity than S. mesatlantica Hc (4.74-5.54 vs 1.83-2.06, respectively).
5.4. MANUSCRIT : RESPIRATORY ADAPTATIONS OF S. MESATLANTICA 201 FIG. 5.13 – L-lactate and pH effect on Segonzacia mesatlantica Hc affinity. Functional parameters P 50 and n 50 were measured at different pH and with several L-lactate concentrations. Experiments were performed at 15°C on physiological saline buffer washed hemocyanin from a single individual. For comparison, data for Hc from the shore crab Carcinus maenas is also presented on the graph (Truchot, 1980). For S. mesatlantica Hc, a second order polynomial was fitted to the P 50 values with 0 mM L-lactate. For fitting to the values in presence of L-lactate, the same equation was used and the value of the constant term was adjusted to minimize the difference with the experimental points. This is valid under the hypothesis that the Bohr effect is not affected by L-lactate, which is false for some species. The value for the L-lactate effect is then calculated from the P 50 values at different L-lactate concentrations interpolated at the same pH.
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5.4. MANUSCRIT : RESPIRATORY ADAPTATIONS OF S. MESATLANTICA 201<br />
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FIG. 5.13 – L-lactate <strong>and</strong> pH effect on <strong>Segonzacia</strong> <strong>mesatlantica</strong> Hc affinity. Functional parameters<br />
P 50 <strong>and</strong> n 50 were measured at different pH <strong>and</strong> with several L-lactate concentrations. Experiments<br />
were performed at 15°C on physiological saline buffer washed hemocyanin from a single individual.<br />
For comparison, data for Hc from the shore crab Carcinus <strong>maenas</strong> is also presented on the graph<br />
(Truchot, 1980). For S. <strong>mesatlantica</strong> Hc, a second order polynomial was fitted to the P 50 values with<br />
0 mM L-lactate. For fitting to the values in presence of L-lactate, the same equation was used <strong>and</strong> the<br />
value of the constant term was adjusted to minimize the difference with the experimental points. This<br />
is valid under the hypothesis that the Bohr effect is not affected by L-lactate, which is false for some<br />
species. The value for the L-lactate effect is then calculated from the P 50 values at different L-lactate<br />
concentrations interpolated at the same pH.