Functional and biochemical properties of the hemoglobins of the burrowing brittle star Hemipholis elongata say (Echinodermata, Ophiuroidea).
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 (P(50) = 11.4 mm Hg at pH 8, 20 degrees C, measured in cellulo) and exhibits cooperativity (Hill coefficient > 1.7). The hemoglobin of juveniles has a higher affinity (P(50) = 2.3 mmHg at pH 8.0, 20 degrees 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.
Christensen
Ana Beardsley
AB
Biology Department, Lamar University, PO Box 10037, Beaumont, Texas 77710, USA. christenab@hal.lamar.edu
Colacino
James M
JM
Bonaventura
Celia
C
D000595:Amino Acid Sequence; D000818:Animals; D004447:Echinodermata / Q000502:physiology*; D006454:Hemoglobins / Q000378:metabolism* / Q000502:physiology*; D007700:Kinetics; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D010100:Oxygen / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D013022:South Carolina
D006454:Hemoglobins; D010100:Oxygen