Kinetics of complex formation between fluorescein mercuric acetate and DNA.

Abstract

AbstractThe kinetics of complex formation between fluorescein mercuric acetate and heat‐denatured DNA were studied by measuring the fluorescence quenching of this reagent. This quenching process involved no immeasurably rapid phase and it was shown that this reaction follows simple second‐order kinetics. The rate constant at 25°C was estimated to be 2.9 × 104M−1 sec−1 for calf‐thymus DNA (42% G + C) and 1.1 × 104M−1 sec−1 for Micrococcus lysodeikticus DNA (72% G + C). Activation parameters for this reaction were calculated from the temperature dependence of the reaction rate, and the activation entropy was found to be highly negative (−27.5 cal/mol deg for calf‐thymus DNA and −25.5 cal/mol deg for M. lysodeikticus DNA). The binding of fluorescein mercuric acetate to native DNA, which requires the opening of the double‐helical structure, was also followed by measuring the absorbance change of this reagent. There was a lag phase in this binding process, and the enthalpy change for the opening step corresponded roughly to that for the opening of one base pair. These findings are discussed in relation to the results of a similar study with formaldehyde.