The association of amphibian (Xenopus laevis) egg yolk platelet
proteins, represented predominantly by
lipovitellin, was studied as a model of the formation of
amyloid deposits. Two kinds of molecular organization formed by this
protein material - native and heat-denatured - were found to exhibit
amyloid properties although they differ significantly in structural organization. The first consisted in
protein molecules arranged in the natural, physiological, net-like platelet organization, with a tendency to orient uni-directionally. The second was obtained by the gradual removal of
Congo red from
lipovitellin denatured by heating in an excess of
dye. This procedure produced the twisted fibrillar organization of molecules typical for amyloids, represented predominantly by end-to-end associated major
polypeptide chains of
lipovitellin. Both native and denatured structural forms bind
Congo red and produce a green birefringence effect, confirming the near parallel alignment of the complexed
Congo red molecules. However, a dye(1,4-bis(1-amino-4-sulfonaphtyl-2-azo)phenylene) closely related to
Congo red but with a very weak self-assembling tendency appeared inactive when the spectral shift was studied in a cross-polarization system, indicating in this way that
dye supramolecularity is an extra factor which may determine binding to
amyloid proteins and specific spectral effects.