NONCOVALENT DNA GROOVE-BINDING BY 2-AMINO-1-METHYL-6-PHENYLIMIDAZO[4,5-B]PYRIDINE

The cooked meat mutagen 2-amino-1-methyl-6-phenyl-imidazo[4,5-b]pyridi ne (PhIP) is metabolized in vivo to electrophilic intermediates that c ovalently bind to DNA guanines. Here we address the mechanism of PhIP' s non-covalent interaction with DNA by using spectroscopic and computa tional methodologies. NMR methodologies indicated that upon addition o f DNA, PhIP aromatic protons underwent a small, 0.11-0.12 p.p.m. upfie ld shift. DNA phosphorus resonances of noncovalent PhIP-DNA complexes broadened and slightly shifted upfield, while DNA base imino proton re sonances shifted slightly downfield relative to DNA alone. UV and fluo rescence spectra of PhIP titrated with DNA showed no detectable shifti ng and hypochromism of absorbance or fluorescence bands. In the presen ce of DNA, PhIP fluorescence was efficiently quenched by acrylamide, b ut not by silver ion. Further, the NMR spectra suggest that PhIP is in fast exchange with the DNA, and is slightly specific for adenine-thym ine (A-T) sequences. Finally, structural arguments based on quantum ch emistry calculations suggested that PhIP and its metabolites are unlik ely to intercalate into DNA. These data collectively indicate that PhI P noncovalently binds in a groove of DNA.