Crystallography of hemerythrin
X-ray crystallographic studies of hemerythrin from Golfingia gouldii show that the molecules pack in a tetragonal cell with two sets of molecules in an apparently face-centred array seen in projection along the 4-fold axis, but displaced relatively to each other by approximately c10 in the axial direction. Both sets of molecules lie on 4-fold rotation axes, so that the subunits of each octameric molecule are related in pairs by a molecular 4-fold rotation axis. The two subunits of each pair are probably related by non-crystallographic 2-fold rotation axes perpendicular to the 4-fold axes and lying at 10 ° and 55 ° to the a and b axes. At low resolution the subunits are apparently arranged approximately in the form of a square prism. Along each 4-fold crystallographic axis there are two hemerythrin molecules, nearly equidistant and having similar but not identical orientations.