Determination of Dissociation Constant of Noncovalent Complex of DNA with L-argininamide Using ESI-FTICR/MS

Electrospray ionization mass spectrometry (ESIMS) has been developed fast in more than one decade and widely used for studies of noncovalent interactions between protein and protein, protein and nucleic acid, as well as biomolecule and drugs. As a result, determinations of binding stoichiometry and binding sites are available. In addition, it has been used for determinations of binding constants. However, precise determinations of binding constants calculated from ion abundances depend on the precise determinations and calculations of gasphase ion abundance. This study selected a well studied 24mer hairpin DNA strand that specifically interacts with L-argininamde as a model studied the relationship of gasphase ion abundances and ion concentrations in varieties of solution (water, fixed concentrations of ammonium acetate, various concentrations of ammonium acetate) using elelctrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR MS) in negative ion mode. The purpose is to determinate dynamic range of multiply charged DNA ions. The binding constants were detected in different ratios of DNA and L-argininamide (1∶1, 1∶2, 1∶3 and 1∶4), the constant obtained in 1∶4 ratio shows good agreement with CD determination, in which both abundances of DNA and DNA L-argininamide complex ions fall in a linear dynamic range. The determination of ion dynamic range and the calculation of multiply charged ion abundance presented in this work will benefit others who intend to detect precise concentrations of multiply charged ions and binding constants of noncovalent complexes.