Interactions between calmodulin and immobilized phenothiazines.

The ability of a number of antipsychotic drugs such as phenothiazines to bind to calmodulin with high affinity in a calcium-dependent manner was applied to the study of the nature of their interactions with calmodulin. Thus, a series of phenothiazine derivatives and analogues were immobilized on agarose and examined for their binding characteristics to calmodulin. The binding of calmodulin to fluphenazine, perphenazine and 7-aminotriflupromazine involved on the one hand non-specific electrostatic interactions which are abolished by increasing the eluent salt concentration, and on the other hand, Ca2+-dependent interactions which are reversed by EGTA addition. However, the Ca2+-dependent binding of calmodulin was less specific with phenothiazine structural analogues (neutral Red, diphenylamine) and was suppressed with other phenothiazine derivatives (thionine, Azure C, Toluidine Blue) or analogues (Brilliant Cresyl Blue). It is suggested that the calcium-dependent interactions between calmodulin and drugs involve a charge transfer pi-pi interaction which may be modulated by the electron donor-acceptor properties of the substituents of the aromatic ring. Affinity chromatography using immobilized fluphenazine was also used as the basis for the purification of calmodulin from a number of tissues in a rapid one-step procedure.