BINDING OF POLYCYCLIC PLANAR MUTAGENS TO CHLOROPHYLLIN RESULTING IN INHIBITION OF THE MUTAGENIC ACTIVITY

Chlorophyllin is known to inhibit the mutagenicity of a variety of com pounds. Using highly purified samples of chlorophyllin and its family compounds, we studied the mechanism of the inhibition. Since mutagens with polycyclic planar structures are particularly strongly inhibited, it seemed likely that the inhibition arises by trapping of the mutage ns by chlorophyllin through complex formation at the planar surfaces o f these molecules. To explore this possibility, we prepared a Sepharos e bearing covalently linked chlorophyllin as ligand, and the adsorptio n of mutagens to this Sepharose was measured. Three different chloroph yllin derivatives were used, i.e., copper-chlorin, iron-chlorin and ch lorin, to investigate the role of metal in the center of the chlorophy llin chromophore. Adsorption of 37 different compounds, mostly mutagen s, in 0.02 M Tris-HCl buffer at pH 8.0 to these chlorophyllin-Sepharos e preparations was studied in a quantitative manner. The results showe d that most of the compounds having three or more fused rings were str ongly adsorbed with apparent dissociation constants of 10(-5)-10(-6) M , whereas those having two fused rings or one ring were only poorly ad sorbed. Since the three Sepharose adsorbents gave similar adsorption p rofiles, it appeared that the central metal in the chlorophyllin molec ule does not play a crucial role in the adsorption. We also measured t he inhibitory effect of copper-chlorin against the mutagenicity of som e-of these compounds using the Salmonella assay. The results showed th at those mutagens that were strongly adsorbable to copper-chlorin-Seph arose were subject to efficient inhibition by copper-chlorin, whereas many of those only poorly adsorbed were inhibited only weakly. We conc luded that trapping by complex formation plays a role in the antimutag enic actions of chlorophyllin against many mutagens, particularly nota ble being the actions against ICR-170, quinacrine, aflatoxin B1, Trp-P -1 and Trp-P-2. An unusual behavior of Trp-P-2 in the adsorption proce ss, i.e., a very tight complex formation at an extremely low Trp-P-2 c oncentration, was found; the implication of this phenomenon in relatio n to the real environmental setting is discussed.