Rate and Rate-Determining Step of Hydrogen-Atom-Induced Strand Breakage in Poly(U) in Aqueous Solution under Anoxic Conditions

Abstract

The rate constant for strand breakage in poly(U) after reaction with hydrogen atoms in deoxygenated aqueous solution has been determined to be k = 1.5 s-1 at pH = 4-5 and 24 °C. Dithiothreitol has been found to prevent strand break formation by reacting with H-adduct radicals of poly(U) with a rate constant of 5 × 106 M-1 s-1. It is concluded that the rate-deter­mining step in H atom-induced strand breakage in poly(U) at pH ≦ 6 is the decay of uracil moiety H-adduct radicals via H-abstraction from the ribose moiety.