DYNAMIC PROPERTIES OF MONOMERIC INSECT ERYTHROCRUORIN-III FROM CHIRONOMUS-THUMMI-THUMMI - RELATIONSHIPS BETWEEN STRUCTURAL FLEXIBILITY AND FUNCTIONAL COMPLEXITY

We have investigated the kinetics of geminate carbon monoxide binding to the monomeric component III of Chironomus thummi-thummi erythrocruo rin, a protein that undergoes pH-induced conformational changes linked to a pronounced Bohr effect. Measurements were performed from cryogen ic temperatures to room temperature in 75% glycerol and either 0.1 M p otassium phosphate (pH 7) or 0.1 potassium berate (pH 9) after nanosec ond laser photolysis. The distributions of the low temperature activat ion enthalpy g(H) for geminate ligand binding derived from the kinetic traces are quite narrow and are influenced by temperature both below and above similar to 170 K, the glass transition temperature. The ther mal evolution of the CO binding kinetics between similar to 50 K and s imilar to 170 K indicates the presence of some degree of structural re laxation, even in this temperature range. Above similar to 220 K the w idth of the g(H) progressively decreases, and at 280 K geminate CO bin ding becomes exponential in time. Based on a comparison with analogous investigations of the homodimeric hemoglobin from Scapharca inaequiva lvis, we propose a link between dynamic properties and functional comp lexity.