Interactions of norharman and harman with DNA

Abstract
The interactions of norharman (9H-pyrido[3,4-b]indole) and harman (1-methyl-9H-pyrido[3,4-b]indolel with DNA were studied. DNA caused remarkable fluorescence quenching and change in the absorption spectra of the dyes. Scatchard plots obtained by optical titration gave Kd values of 2.2 × 10 −5 M and 7.7 × 10 −6 M, and apparent numbers of binding sites of 0.13/base and 0.12/base for norharman and harman, respectively. Agarose gel electro-phoresis of circular DNA, closed in the presence or absence of norharman revealed that the dye intercalates DNA, thereby causing 17 ± 3° unwinding of the double helix.