We study the problem of pseudoscalar mixing in an SU(4)xSU(4)xUA(1) breaking framework. In this connection, we derive the condition of a vanishing cc̄ component in the η,η′ wave functions. We also obtain new constraints obeyed by the mixed decay constants fη,η′q (q=u,s), which determine the octet-singlet mixing angles. In the ηη′ ηc sector we find from a fit to the radiative decay rates of mesons that the presence of a cc̄ admixture in η′ is small in disagreement with the point of view that the branching ratio of B→η′ K is enhanced by η′ ηc mixing. ©1999 The American Physical Society.