[Interactions between pigments and nucleic acids. 4. Specific and non specific complexes between luteoskyrine, magnesium ions, and nucleic acids].

Abstract

Luteoskyrine, a bis‐polyhydroxyanthraquinone, is a toxic pigment produced by Penicillium islandicum . Its ingestion results in hepatomas and cirrhotic degeneration of the liver in man and the rat. This pigment is able to form in vitro and in the presence of Mg 2+ ions two types of complexes with DNA. The first (I) and rapidly formed complex corresponds to an interaction with the purines of the DNA. To react luteoskyrine with the DNA purines, the DNA must be denatured. The interaction is established by the following criteria: In the presence of denatured DNA the insoluble luteoskyrine‐Mg 2+ complex is not formed. The spectrum of luteoskyrine in aqueous solution is shifted to shorter wave lengths. When submitted to ultracentrifugation and analysed at 260 mμ, and at 450 mμ the denatured DNA and the luteoskyrine sediment at the same rate, and the sedimentation coefficient of the complex is greater than that of the same sample of DNA alone. After addition of luteoskyrine and magnesium ions, partially structured DNA is stabilized against further heat denaturation. Similar complexes (type I) are also formed with poly A, poly G and poly I. In each case, the spectra obtained and their stability are characteristic of the polymer utilised. Therefore the complexes of type I are said to be specific. The second type of complex, type (II), on the contrary, is made slowly with native DNA or paired ribopolymers (poly A:U or poly G:C) irrespective of the nature of the constituent bases. Type II complexes can also be slowly formed from the type I complexes first made with denatured DNA. The spectra of the type II complexes are not characteristic of the nucleic acids involved but are very similar to those corresponding to the aggregated luteoskyrine‐Mg 2+ complex.