The structure of haemoglobin. II

Abstract

The outer form of the haemoglobin molecule is delimited by considering the way in which it packs into a number of crystalline forms. A simple spheroidal form of the molecule is found to account for the lattice dimensions with a remarkable degree of consistency. The dimensions of the spheroid are 53 x 53 x 71 Ǻ in the case of the hydrated molecule, and 45 x 45 x 65 Ǻ in the case of the dry molecule, with an error of less than 2 Ǻ in each direction. The evidence of form birefringence is compatible with these conclusions. They are supported by observed changes in diffraction effects with salt concentration. The spheroidal shape can only be a first approximation, and the protein molecule must be more polyhedral in shape, since in the dry form it occupies a considerably larger proportion of the total volume than would be occupied by spheroids in close packing. The limits to its form which are set by packing contacts are defined.