Molecular symmetry of Lumbricus erythrocruorin.

X-ray diffraction data to a minimum Bragg spacing of 5.5 A have been collected from crystals of Lumbricus terrestris erthrocruorin, a 3.9 x 10(6)-dalton respiratory protein. Self-rotation function calculations from these data reveal D6 symmetry to a resolution of at least 6 A. These calculations show that erythrocruorin molecules pack in their crystals with molecular diads coincident with crystallographic diads along the a axis. Packing constraints limit the position of the molecular center to within 40 A of x = 1/4a.