CIRCULAR DICHROIC AND SPECTROPHOTOMETRIC PROBES OF THE COMPETITIVE-BINDING OF CRYSTAL VIOLET BETWEEN DNA AND OTHER ANIONIC POLYMERS

Of the two synthetic polyanions poly-(styrene sulfonate) (PSS) and pol y-(vinyl sulfate) (PVS), the latter induces sharper metachromasia in t he cationic dye crystal violet (CV); DNA, however, fails to induce met achromasia in the dye. Contrary to speculation, DNA binds CV, though a nonintercalating dye, rather strongly and holds a portion of the dye even in the presence of PSS or PVS, which induces strong metachromasia . Induced circular dichroism (ICD) in CV by DNA shows that DNA binds C V, and partial reduction of ellipticity of DNA-CV by PVS shows that CV distributes itself between the two polyanions. DNA is shown to be the winner in the competitive binding of CV even with the strong polyanio n heparin (Hep) as the competitor. This has been interpreted as being due to the binding of CV to DNA, primarily by ionic attraction stabili zed further by nonionic forces like H-bonding in the grooves of DNA. Q uantitative estimations of the association constants of DNA-CV and PVS -CV by Scatchard plot come to 0.74 X 10(6) and 1.28 x 10(6) l mol-1, r espectively.