Sensitivity of P-glycoprotein tryptophan residues to benzodiazepines and ATP interaction |
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Authors: | Lima Sofia A C Cordeiro-da-Silva Anabela de Castro Baltazar Gameiro Paula |
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Institution: | REQUIMTE, Departamento de Química da Faculdade Ciências da Universidade do Porto, Porto, Portugal. |
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Abstract: | Plasma membrane P-glycoprotein is a member of the ATP-binding cassette family of membrane transporters. In the present study tryptophan intrinsic fluorescence was used to understand the P-glycoprotein response to three benzodiazepines (bromazepam, chlordiazepoxide and flurazepam) in the presence and absence of ATP. Fluorescence emission spectra showed a red shift on the maximal emission wavelength upon interaction of P-glycoprotein with all benzodiazepines. Benzodiazepine association with nucleotide-bound P-glycoprotein also showed this trend and the quenching profile was attributed to a sphere-of-action model, for static fluorescence. Furthermore, quenching data of benzodiazepine-bound P-glycoprotein with ATP were concentration dependent and saturable, indicating that nucleotide binds to P-glycoprotein whether drug is present or not. These results seems in agreement with the proposal of the ATP-switch model by Higgins and Linton, where substrate binding to the transporters initiates the transport cycle by increasing the ATP binding affinity. |
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Keywords: | P-glycoprotein Intrinsic fluorescence Benzodiazepines ATP Interactions |
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