Crystallographic study of the ferritin molecule: new results obtained from natural crystals in situ (mollusc oocyte) and from isolated molecules (horse spleen).

The aim of the present work is to gather new information on the ferritin molecule. Natural crystals of ferritin occurring in the yolk platelets of a mollusc oocyte were studied. Their crystallographic structure was found to be equivalent to one of the structures obtained by artificial crystallization (fcc; a = 15 nm). Individual ferritin particles isolated from horse spleen were studied by microdiffraction techniques, using field emission gun transmission electron microscopy. The iron core crystals display a hexagonal structure; our results confirm the value of the unit cell parameter a (0.51 nm) and, for the first time, we have been able to extract the value of the unit cell parameter c (0.95 nm). Thus, among the three models described in the literature for the crystalline structure of the iron complex, our results corroborate that of Towe and Bradley (J. Colloid. Interf. Sci., 1967, 25, 384-392).