The stability and transitions of tryptic-digested clathrin.

The pH-dependence of dissociation of trypsin-digested baskets has been determined by light scattering and compared with that of undigested baskets. Essentially no difference was found between the two types of baskets. The molecular transitions of clathrin derived from digested baskets have been studied by fluorescence spectra and polarization measurements and compared with those of undigested baskets. The transitions in both forms of clathrin were very similar. It is clear, therefore, that removal of about 1/3 of the mass from the distal portions of the arms of the clathrin triskelion does not affect its structural transitions. The interactions between clathrin molecules in the basket structure and those within the molecule appear, therefore, to remain intact in the smaller clathrin chains remaining after tryptic digestion. The function of the distal portion of the clathrin chain still awaits elucidation.