Further insight into the Zn2+-mediated binding of streptonigrin to DNA

The interaction of double- and single-stranded DNA with the antitumor antib iotic streptonigrin (STN) in the presence of zinc ions has been examined by spectrophotometric and circular dichroism techniques. Very little interact ion occurs in the absence of the metal ion. When Zn2+ is present, the bindi ng process exhibits a bell-shaped dependence upon the ion concentration, co nsistent with the formation of a ternary complex, splitting into two binary complexes at high content of the metal ion. Evidence is presented for the participation of two STN molecules bridged by Zn2+ in the complex with DNA. (C) 1998 Elsevier Science S.A. All rights reserved.