Murex trunculus Haemocyanin

Abstract

The oxygenation of Murex trunculus haemocyanin was studied over a range of pH values and Mg2+ concentrations by following the increase in absorption at 346 nm as oxygen was bound. In the absence of Mg2+ the oxygen‐binding curves appeared to be hyperbolic, n in the Hill plots was approximately unity, and there was no appreciable Bohr effect. In the presence of Mg2+ the Hill plots showed a number of slopes and there was a marked, reverse Bohr effect. Deoxygenation of a solution haemocyanin at pH 9.9 in the presence of 0.01 M Mg2+, consisting of about 95%, wholes and 5%, halves, resulted in dissociation to 63.2% wholes and 36.8%, halves, and this dissociation was slowly reversible upon re‐oxygenation. Changes in oxygenation state were accompanied by changes in the circular dichroism spectrum. Upon deoxygenation, the bands at 346, 480 and 560 nm of the copper · oxygen complex were abolished but there was little change in the doublet at 210–222 nm. However, the positive band at ∼250 nm approximately doubled in intensity.