Crystals of Lumbricus erythrocruorin

Lumbricus terrestris erythrocruorin, a 3.9 X 10(6) Mr respiratory protein, has been crystallized in four different forms. Despite the high molecular symmetry apparent from images in electron micrographs, only one crystal form expresses any molecular symmetry as crystallographic symmetry. The lattice parameters provide upper limits on the molecular dimensions of 267 A X 308 A X 172 A (1 A = 0.1 nm), which agree well with dimensions obtained from electron micrographs of negatively stained molecules. We have collected diffraction data to 5.5 A from type III crystals and have begun a structural analysis.