Rapid communication Protonation effect on drug affinity

Pharmacologic ligand-macromolecule interactions are commonly characterized by affinity (dissociation) constants such as Kd or Ki without regard to the protonation effect of the buffer used in the measurement. The protonation effect is demonstrated here using isothermal titration microcalorimetry measurements of the competitive inhibitor binding of cytidine 2V-monophosphate (2V-CMP) to RNase-A as a model system in buffers of different ionization DHbuffer. The results demonstrate the importance of protonation in measures of affinity. D 2003 Elsevier B.V. All rights reserved.