title: Chlorpromazine binding to Na+, K+-ATPase and photolabeling: involvement of the ouabain site monitored by fluorescence.
abstract: This work reports the results of ultraviolet irradiation on the interaction of the phototoxic antipsychotic drug chlorpromazine (CPZ) with the sodium pump Na+, K+-ATPase. The study was performed by monitoring the fluorescence modifications of CPZ itself and of the specific probe anthroylouabain (AO). CPZ association with Na+, K+-ATPase was found to modify the kinetics of CPZ-photodegradation. It was demonstrated that UV irradiation produces a stable fluorescent photoproduct of CPZ covalently bound to Na+, K+-ATPase. The fluorescent probe AO, which specifically binds to the extracellular ouabain site of the pump, was used to localize the CPZ binding site. UV-irradiation of AO-labeled Na+, K+-ATPase treated with CPZ at concentration about 20 microM produced dose-dependent modifications of the AO fluorescence, e.g. increased quantum yield and blue shift. The results demonstrated that CPZ binds near the ouabain site. The photo-induced reaction of CPZ with AO-labeled Na+, K+-ATPase protected the ouabain site from the aqueous environment. It was also found that UV irradiation of CPZ-treated enzyme obstructs the binding of AO, which suggested occlusion of the ouabain site. This effect can be evaluated for a potential use of CPZ in photochemotherapy.
authors.affiliation: Department of Physics, Pontifícia Universidade Católica do Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Elmer A C
authors.initials: EA
authors.lastname: Guevara
authors.forename: Maria
authors.initials: M
authors.lastname: de Lourdes Barriviera
authors.forename: Aída
authors.initials: A
authors.lastname: Hassón-Voloch
authors.forename: Sonia R W
authors.initials: SR
authors.lastname: Louro
mesh_terms: D014150:Antipsychotic Agents / Q000378:metabolism*; D001665:Binding Sites; D002746:Chlorpromazine / Q000378:metabolism*; D010042:Ouabain / Q000378:metabolism*; D010777:Photochemistry; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
chemical_list: D014150:Antipsychotic Agents; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D002746:Chlorpromazine