SMALL-ANGLE X-RAY-SCATTERING STUDIES ON THE POLYDISPERSITY OF IRON MICELLES IN FERRITIN

Small-angle X-ray scattering was applied to study the structure of hor se-spleen ferritin and apoferritin as well as of various intermediate states differing in their iron content. The intermediates were produce d by partial removal of iron from ferritin or by incorporation of iron into apoferritin. Measurements were performed in dilute buffer and in 66% (w/v) sucrose solution. The scattering curves were analysed in te rms of radii of gyration, R(G), distance distribution functions, p(r), and size distribution functions, D(V)(R). The results reflect charact eristic changes of R(G) and of p(r) upon release or uptake of iron and suggest a bimodal polydisperse size distribution of iron micelles in ferritin. The interpretation of data was paralleled by computer simula tions based on various different models.