Structure and properties of hemocyanins. I. Electron micrographs of hemocyanin and apohemocyanin from Helix pomatia at different pH values.

Abstract

Electron micrographs were made from Helix pomatia hemocyanin at different pH values with the negative-staining method. The pH-dependent dissociation on the alkaline side of the isoelectric point was especially studied. Our observations are in agreement with previously reported results, although they are not compatible with the model and mechanism of dissociation previously proposed. Our observations suggest that the Helix pomatia hemocyanin molecule is roughly cylindrical ; the diameter of the cylinder is about 300 A and the height is about 335 A. This cylinder has a fivefold axis; perpendicular to this axis it is built up from 6 parallel layers. The first dissociation step occurs perpendicular to the fivefold axis into halves. Further dissociation is supposed to be a splitting of these flat cylinders via submultiples into subunits. Divalent cations in concentrations of about 10−4 molar or higher are required for the reversibility of this dissociation. Helix pomatia apohemocyanin shows a similar behaviour.