Biochemistry of Hemoglobin and Oxygen Transport

University Of Texas At Austin, Austin TX

Investigators

Abstract

This project concerns four hemoglobins from (1) earthworm,(2) chicken and hummingbird, (3) lamprey, and (4) the nemertean worm, Cerebratulus. The ligand-dependent dissociation of each hemoglobin is to be studied by light-scattering and sedimentation. Earthworm hemoglobin is a ~4.1 MDa, 200 subunit complex with both Hb subunits and non-globin components. The assemblage gradually loses subunits and the mass decreases to 3.6 MDa. A first goal is the mechanism for this stoichiometric conversion. A second goal is to determine the seasonal changes in the biosynthesis of the Hb and to determine if the Hb is synthesized only in the spring of the year. Ongoing studies on chicken hemoglobins have shown that two components of chicken hemoglobin, A and D, associate upon deoxygenation to form an assemblage of low oxygen affinity and enhanced cooperativity. The project will determine the stoichiometry and mass of the assemblage and the functional relationship between oxygenation and the dissociation of the A-D assemblage. Another goal of this project is the determination of the kinetics and equilibria of ligand binding of hummingbird hemoglobin to assess the extent to which the Hb is adapted to meet extraordinary physiological needs. Lamprey hemoglobin self-associates from monomer to dimer upon deoxygenation. The functional interaction of groups at the interface between the subunits will be studied with site-specific mutagenesis. Cerebratulus hemoglobin, with only 109 residues, is the smallest known hemoglobin. Collaborative studies of ligand-binding kinetics and equilibria will be undertaken with a variety of mutants constructed by site-specific mutagenesis. Broader Impact: The past activities in this project have involved outstanding training of undergraduate researchers and the future research will continue to provide such opportunities.