Relaxation kinetics of the interaction between RNA and metal-intercalators: The Poly(A)·Poly(U)/platinum-proflavine system

Abstract

The interactions of Poly(A)·Poly(U) with the cis-platinum derivative of proflavine [{PtCl(tmen)} 2{HNC 13H 7(NHCH 2CH 2) 2}] + (PRPt) and proflavine (PR) are investigated by spectrophotometry, spectrofluorimetry and T-jump relaxation at I = 0.2 M, pH 7.0, and T = 25 °C. Base–dye interactions prevail at high RNA/dye ratio and binding isotherms analysis reveals that both dyes bind to Poly(A)·Poly(U) according to the excluded site model ( n = 2). Only one relaxation effect is observed for the Poly(A)·Poly(U)/PRPt system, whereas two effects are observed with Poly(A)·Poly(U)/PR. The results agree with the sequence D + S ⇆ D, S ⇆ DS I ⇆ DS II, where D,S is an external complex, DS I is a partially intercalated species, and DS II is the fully intercalated complex. Formation of DS II could be observed in the case of proflavine only. This result is interpreted by assuming that the platinum-containing residue of PRPt hinders the full intercalation of the acridine residue.