 It appears to be easily dissociable, and it has been shown that hexamers accumulate when magnesium is removed "in vitro".Though it is not common to consider hydronium ions as allosteric regulators, in the case of PBGS, side chain protonation at locations other than the active site has been shown to affect the quaternary structure equilibrium, and thus to affect the rate of its catalyzed reaction as well.Inspection of the PBGS 6mer* reveals a surface cavity that is not present in the 8mer.