Affiliation:
1. Institute of Biology, Odense University, Campusvej 55, DK-5230 Odense M, Denmark. fbj@biology.ou.dk.
Abstract
Agnathans, comprising lamprey and hagfish species, have been reported to be practically devoid of HCO3-/Cl- exchange across the red blood cell membrane. This suggests that the capacity of their haemoglobin (Hb) to remove H+ is essential for obtaining a high CO2-carrying capacity in the blood. Hydrogen ion titrations were performed on oxygenated and deoxygenated composite Hbs from river lamprey and from Atlantic hagfish at 15 degrees C and an ionic strength of 0.1 (0.1 mol l-1 KCl). Lamprey Hb was characterised by very low buffer values when the degree of oxygenation was constant, whereas the fixed-acid Haldane effect was large (uptake of approximately 0.9 H+ per monomer upon deoxygenation). Hagfish Hb, in contrast, had large buffer values and a moderate fixed-acid Haldane effect. In deoxygenated Hb, the low buffer values in lamprey correlated with the presence of only 1–1.5 titratable ‘neutral’ groups (normally histidines and α -amino groups) per monomer, whereas there were 4–5 titratable ‘neutral’ groups per monomer in hagfish. The large differences in Hb/H+ equilibria between the two species reflect the early evolutionary divergence between lampreys and hagfish. With respect to CO2 transport, the special Hb/H+ equilibria and the high red blood cell pH in lamprey ensure a high concentration of free HCO3- inside the red cells in venous blood, which compensates for the absence of a shift of HCO3- to the plasma. The Hb/H+ equilibria in hagfish are less effective in ensuring a high CO2-carrying capacity given the virtual absence of a red blood cell HCO3-/Cl- exchange, and other adaptations may be involved.
Publisher
The Company of Biologists
Subject
Insect Science,Molecular Biology,Animal Science and Zoology,Aquatic Science,Physiology,Ecology, Evolution, Behavior and Systematics
Cited by
5 articles.
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