DNA: reaction with chloroquine.

Diflerence spectrophotometry shows that double-stranded DNA produces mnarked changes in the absorption spectrum of chloroquine; only minor changes occur with single-stranded DNA. A DNA-chloroquine complex was demonstrated to sediment in the analytical ultracentrifuge. Chloroquine strongly elevated the thermal dissociation temperature, T(m), of DNA. It is concluded that the drug forms a complex with DNA by ionic interaction and stabilizes the helix.