  We study the behavior of two macroions with dissociable charge groups,
regulated by local variables such as pH and electrostatic potential, immersed
in a mono-valent salt solution, considering cases where the net charge can
either change sign or remain of the same sign depending on these local
parameters. The charge regulation, in both cases, is described with the proper
free energy function for each of the macroions, while the coupling between the
charges is evaluated on the approximate Debye-H\"uckel level. The charge
correlation functions and the ensuing charge fluctuation forces are calculated
analytically and numerically. Strong attraction between like-charged macroions
is found close to the point of zero charge, specifically due to asymmetric,
anticorrelated charge fluctuations of the macroion charges. The general theory
is then implemented for a system of two protein-like macroions, generalizing
the form and magnitude of the Kirkwood-Schumaker interaction.
