Fig. 6.

Schematic structure of insulin spherulites. (A) Optical microscopy image of a spherulite recorded after the insertion of a wave plate. The double-headed arrow indicates the orientation of the fast optical axis of the wave plate. (Scale bar, 50 μm.) (B) Schematic representation of the proposed structure of the spherulites. The expanded picture shows individual fibrils illustrating that the β-strands that assemble to form sheets are oriented perpendicular to the fibril axis. A theoretical wave plate, superimposed onto this picture in the same orientation as in A, would result in the fast axis of the fibrils, the protein backbone, being perpendicular to the fast axis of the wave plate, resulting in the yellow color seen in A.