Bisulfite ion-catalyzed transamination of cytosine residues with .alpha.,.omega.-alkanediamines: The effect of chain length on the reaction kinetics

Pseudo-first-order rate constants for the bisulfite ion-catalyzed transamination of cytidine with 1,2-ethanediamine, 1,3-propanediamine, 1,4-butanediamine, and 1,6-hexanediamine have been determined. Hydrolytic deamination has been shown to compete with transamination under acidic conditions, but is of minor importance at pH > 5.3 when the total concentration of diamine is greater than 0.2 mol dm-3. The dependence of the transamination rate on pH and the concentration of diamine and bisulfite ion indicates that the major reaction involves nucleophilic attack of the diamine monocation on the N3 protonated bisulfite adduct of cytidine. The effect of the chain length of the diamine on the rate of transamination is discussed, and the results are compared with those obtained by reacting single-stranded DNA with the same diamines and labeling the transaminated product with a europium chelate.