The Oxygenation of Hemoglobin in Lugworms

Abstract

The extracellular hemoglobin found in the closed circulatory system of lugworms has a high oxygen affinity and extremely great cooperativity in oxygen binding. These properties are not accompanied by low oxygen levels in the microhabitat so long as ventilation continues. The quantitative function of lugworm hemoglobin is greatest at the intermediate and high oxygen levels created in the burrow by maximum ventilation activity. The distinctive oxygenation properties are related to operating conditions in the blood vessels. The large amount of mixing of post- and prebranchial blood in this primitive circulatory system results in low blood PO₂'s and little PO₂ difference between afferent and efferent blood. The Bohr shift is functional, but its role in oxygen transport is small. The primary function of lugworm hemoglobin is oxygen transport at high tide. At both low and high acclimation temperatures, an appreciable fraction of the oxygen consumed (15%-45%) is carried by hemoglobin.