Birefringence of protein solutions and biological systems. II. Studies on TMV, tropocollagen, and paramyosin

The intrinsic birefringences of TMV, tropocollagen, and paramyosin were calculated from flow birefringence measurements using the theory of Peterlin and Stuart. The values are -0.029, -0.029, and -0.030, respectively. The intrinsic birefringences of TMV and tropocollagen were measured as a function of the refractive index of the solvent in glycerol-water mixtures. In both cases the values were not constant and became less negative as the refractive index increased. Theoretical calculations showed that the large solvent effect could not be caused by a hydration shell of index different from that of the bulk solvent. It is concluded that either (a) the intrinsic birefringence calculated from the Peterlin-Stuart theory is incorrect or (b) the intrinsic birefringence depends markedly on the solvent. These results are of importance to the problem of quantitative polarized light microscopy since the separation of form and intrinsic birefringence contributions is based on the assumption that intrinsic birefringence is independent of solvent.