The electrophoresis of a charge-regulated spherical particle normal to a planar surface is analyzed theoretically. The present study extends previous analyses in that the surface of the particle assumes a general charged condition, which simulates biocolloids and particles covered by an artificial membrane, and an arbitrary, double layer thickness kappaa, kappa, and a being respectively the reciprocal Debye length and particle radius. We conclude that the thinner the double layer and/or the larger the particle-surface distance, the greater the mobility of the particle. If the concentration of the dissociable functional groups on particle surface N-s is low, the absolute mobility of a particle decreases with the increase in kappaa, and the reverse is true if N-s is high. For a medium N-s, the absolute mobility has a local maximum as kappaa varies. We show that the higher the pH of the liquid phase, the smaller the absolute mobility.