The Turbidity of Cell Nuclei in Suspension: A Complex Case of Light Scattering

The turbidity of a suspension of cell nuclei isolated from animal tissue homogenates is a complex case of non-Rayleigh scattering. As a first approximation to this system, we have characterized a number of factors that may contribute to the observed turbidity: cation-dependent chromatin condensation, thermal denaturation of chromatin, nuclear shrinking, and changes in the optical properties of the membrane bilayer. Small differences in cation concentration, particularly in the case of divalent cations, lead to large changes in chromatin supramolecular organization, thus to large turbidity effects; thermally-induced changes in turbidity have a similar origin, although they are less pronounced. Under certain circumstances, either salts or heat may induce condensation of chromatin, the latter being connected to the inner side of the nuclear envelope, nuclear shrinking ensues, and this in turn modifies the suspension turbidity. Finally, changes in the physical properties of the lipid bilayers or of the phospholipids in the nuclear envelopes may also have significant effects, though smaller than chromatin changes, in the overall turbidity of the nuclear suspension.