The Oxygen Equilibrium of Murex trunculus Haemocyanin
The oxygen-binding properties of Murex trunculus haemocyanin were described briefly by Wood and Dalgleish (1973) in a previous study from this laboratory. In the absence of divalent ions in the pH range 7.2–9.2, noncooperative oxygen binding and a small reverse Bohr effect were observed. In the presence of Mg2+, cooperative oxygen binding (with a Hill coefficient as large as 3 or more in some cases) and a more pronounced Bohr effect were seen. In a later study 50,000 molecular weight fragments (“Oxygen-binding domains”) of the haemocyanin, obtained by subtilisin digestion, were shown to bind oxygen noncoopera- tively, without a Bohr effect and with significantly decreased oxygen affinity with respect to untreated haemocyanin (Bannister et al., 1975). We describe here a systematic study of the oxygen equilibrium of Murex trunculus haemocyanin under various conditions of pH, divalent ion concentration and ionic strength. Oxygen-binding data are analysed in relation to cooperativity and linkage phenomena.
KeywordsMagnesium Titration Sedimentation Carbon Monoxide Macromolecule
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