Attempts of Resolution of the Subunit Structure of Ferritin and Apoferritin by Electronmicroscopy

Abstract

Ferritin is a high molecular weight protein (462,000), composed of 20 apparently identical subunits which form a hollow shell 120 Å in diameter (Harrison). High resolution electron micrographs reveal a dense core (Fig. 1) containing variable amounts of iron hydroxyphosphate complex surrounded by a shell of protein. The protein becomes visible by the use of negative staining in which it appears as a ring structure, the center being overlaid by the dense core (Fig. 2). X-ray diffraction (Harrison) suggested that the subunits are arranged in the form of a dodecahedron (Fig. 5). During the course of our work it became desirable to visualize directly the fine structure of the ferritin and apoferritin molecules in order to follow structural alterations which might occur in different cell compartments, particularly during the transformation of ferritin to hemosiderin in digestive vacuoles.