The role of extracellular hemoglobins in the oxygen consumption of the burrowing polychaete, Euzonusmucronata (Treadwell)

Abstract

The polychaete annelid Euzonus mucronata (Treadwell), which burrows vertically in sandy beaches in response to diurnal tides, encounters daily changes of oxygen tension, salinity, and temperature. Although the animal is capable of long-term (20 days) anaerobiosis it also contains abundant hemoglobin, 19% of dry body wt, which suggests a role for this protein in the maintenance of aerobic metabolism. Approximately 21–29% of the oxygen obtained by E. mucronata is via its extracellular hemoglobins at oxygen tensions down to 1 ml O 2·1 −1 (10°C). These hemoglobins have a relatively high oxygen affinity ( P 1 2 = 1.2 Torr at 10°C) which is insensitive to changes in pH and ion concentration but is influenced by temperature, ΔH = − 12 kcal·mol −1. We suggest that the high affinity of Euzonus hemoglobin and its insensitivity to changes in ion concentration and pH could help the animal to rely mainly on aerobic metabolism throughout most of the tidal cycle.