Dynamic properties of monomeric insect erythrocruorin III from Chironomus thummi-thummi: relationships between structural flexibility and functional complexity

We have investigated the kinetics of germinate carbon monoxide binding to the monomeric component III of Chironomus thummi-thummi erythrocruorin, a protein that undergoes pH-induced conformational changes linked to a pronounced Bohr effect. Measurements were performed from cryogenic temps. to room temp. in 75% glycerol and either 0.1 M potassium phosphate (pH 7) or 0.1 potassium borate (pH 9) after nanosecond laser photolysis. The distributions of the low temp. activation enthalpy g(H) for germinate ligand binding derived from the kinetic traces are quite narrow and are influenced by temp. both below and above .apprx.170 K, the glass transition temp. The thermal evolution of the CO binding kinetics between .apprx.50 K and .apprx.170 K indicates the presence of some degree of structural relaxation, even in this temp. range. Above .apprx.220 K the width of the g(H) progressively decreases, and at 280 K germinate CO binding becomes exponential in time. Based on a comparison with analogous investigations of the homodimeric Hb from Scapharca inaequivalvis, we propose a link between dynamic properties and functional complexity. [on SciFinder (R)]

Published in:
Biophysical Journal, 73, 5, 2742-2751

 Record created 2006-02-27, last modified 2018-01-27

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