Respiratory properties of haemoglobins from eunicid polychaetes

Summary

The extracellular haemoglobins of the sublittoral, mediterranean polychaetesDiopatra neapolitana, Lumbrinereis tetraura andOenone fulgida, representing three different subfamilies of the family Eunicidae, were studied.

• 2. On cellulose acetate electrophoresis strips,Diopatra andOenone haemoglobins are homogeneous, andLumbrinereis haemoglobin resolves into two components.

• 3. Lumbrinereis haemoglobin has the highest oxygen affinity, the largest Bohr effect, and the Hill coefficientn—which reflects the cooperativity between the oxygen-binding haem groups—is strongly pH dependent attaining a high value of 5 at alkaline pH (Fig. 3). The oxygen affinity and corresponding pH sensitivities are lowest inOenone (Fig. 4) and intermediate indiopatra (Fig. 2). In each speciesn is heterogeneous, being higher at high than at low oxygen saturation.

• 4. Water turbulence and median grain size of the sediments at the sites of collection indicate that factors other than low ambient oxygen tensions account for the high oxygen affinity and pH sensitivity of the haemoglobin inLumbrinereis.

• 5. The effect of temperature onP ₅₀ ofLumbrinereis haemoglobin indicates an apparent heat of oxygenation, ΔH of about −11.5 kCal·mole⁻¹ at pH 7.0 and 7.7, showing no adaptive distinction from more eurythermal intertidal eunicid polychaetes.

• 6. The possible adaptive significance of the oxygenation properties of the haemoglobins is discussed.