Experimental differential light-scattering correction to the circular dichroism of bacteriophage T2.

Experimental techniques are presented that can be used to assay and correct for differential light scattering effects in circular dichroism spectra of biological macrostructures. The assay is based upon use of variable detector geometries that collect light over large solid angles. Disrupted T2 virus suspensions and purified T2 phage DNA exhibit geometry-independent spectra; the spectrum of intact T2 virus is highly sensitive to detection geometry. On the basis of spectra obtained after light-scattering correction, the structure of T2 DNA in the phage particle is assigned to the C form. We conclude that: (i) The measured circular dichroism of a light-scattering specimen may be highly sensitive to light-detection geometry of the instrument. This effect is indicative of differential scattering intensity for left and right circularly polarized light. (ii) Some optically active particles, although they scatter light intensely, exhibit circular dichroism that is independent of detection geometry and, therefore, apparently uninfluenced by differential light scattering. We infer that whether differential light scattering arises may depend upon the presence or absence of ordered asymmetry in the organization of the scattering particle. (iii) The circular dichroism of any light-scattering specimen should be measured again in apparatus designed for differential light-scattering correction as a prerequisite to meaningful structural conclusions. (iv) Differential scattering effects in circular dichroism may be potentially useful as a probe for large-order organization of the scattering particle.