A STUDY OF METALLOPORPHYRIN-POLYNUCLEOTIDE INTERACTIONS BY MICROCALORIMETRY AND CIRCULAR-DICHROISM

In this paper we examine the interactions of Calf Thymus DNA and the m odel polynucleotides poly(dA).poly(dT), poly(dAdT)(2) and poly(dG.dC)( 2) with a group of metalloporphyrins derived from the freebase porphyr in tetrakis(4-N-methylpyridyl)porphine, H-2(TMpy-P4), by means of ultr aviolet absorption spectroscopy, circular dichroism spectroscopy and m icrocalorimetry. We have studied the interactions of the copper, cobal t, nickel and zinc derivatives of H-2(TMpy-P4) in addition to the free base porphyrin itself. We have found strong evidence for an external self-stacking interaction of the Cu(TMpy-P4) and Zn(TMpy-P4) derivativ es with poly(dA).poly(dT) and poly(dAdT)(2) even at low concentrations of porphyrin, and all of the porphyrin derivatives studied appear to display such a self-stacking in interaction with poly(dA.dT)(2) at suf ficiently high ratios of porphyrin to polynucleotide.