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Biol. Bull. 205: 54-65. (August 2003)
© 2003 Marine Biological Laboratory

Functional and Biochemical Properties of the Hemoglobins of the Burrowing Brittle Star Hemipholis elongata Say (Echinodermata, Ophiuroidea)

Ana Beardsley Christensen1,*, James M. Colacino2 and Celia Bonaventura3

1 Biology Department, Lamar University, PO Box 10037, Beaumont, Texas 77710
2 Department of Biology, Clemson University, 132 Long Hall, Clemson, South Carolina 29634
3 Marine Biomedical Laboratory, Duke Marine Laboratory, Duke University, 135 Duke Marine Lab Road, Beaufort, North Carolina 28516

* To whom correspondence should be addressed. E-mail: christenab{at}hal.lamar.edu

The burrowing brittle star Hemipholis elongata (Say) possesses hemoglobin-containing coelomocytes (RBCs) in its water vascular system. The RBCs, which circulate between the arms and body, are thought to play a role in oxygen transport. The hemoglobin of adult animals has a moderate affinity for oxygen (P50 = 11.4 mm Hg at pH 8, 20 °C, measured in cellulo) and exhibits cooperativity (Hill coefficient > 1.7). The hemoglobin of juveniles has a higher affinity (P50 = 2.3 mmHg at pH 8.0, 20 °C) and also exhibits cooperativity. The oxygen-binding properties of the hemoglobin are relatively insensitive to pH, temperature, and hydrogen sulfide. Adult hemoglobin is a heterogeneous mixture composed of three major fractions. The combined results of electrospray mass spectrometry and oxygen-binding experiments performed on purified fractions indicate that the native hemoglobin is in the form of homopolymers. A partial amino acid sequence (about 40 amino acids) of adult hemoglobin reveals little homology with holothurian hemoglobins.

Abbreviations: RBCs, red blood cells • WVS, water vascular system






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