Conformational Differences Between Oxy- and Deoxy-Hemocyanin
As in the case of hemoglobin (1)the classic two-state allosteric model (2),based on the presence of two functionally relevant quaternary states of the macromolecule in chemical equilibrium, is often adequate to describe cooperative effects in the binding of O2 by hemocyanin (3,4). Nevertheless direct physical evidence for the presence of different conformational states of hemocyanin in equilibrium is (at best) very limited, with the possible exception of some observations(5,6). Recent spectroscopic studies have shown that upon binding of O2 at the active site of hemocyanin the Cu-Cu distance and the number of ligands (7) bound to the metal atoms change, with a strong involvement of the endogeneous protein bridge. This probably triggers the quaternary conformational change(s) involved in the cooperative binding of 02. In order to aquire direct experimental information on the ligand linked conformational transition of hemocyanins we have applied autocorrelation spectroscopy to probe the internal mobility and the hydrodynamic properties of oxy and deoxy Helix p. β -hemocyanin (M.14.9 millions).
KeywordsAnisotropy Tryptophan Autocorrelation Macromolecule Rhodamine
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