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Phototoxicity of phenothiazine derivatives. II. Photosensitized cross-linking of erythrocyte membrane proteins
Authors:M.P. Merville  J. Piette  J. Decuyper  C.M. Calberg-Bacq  A. Van De Vorst
Affiliation:1. Laboratories of General and Medical Microbiology, Institute of Pathology (B23), University of Liège, B-4000 Liège Belgium;2. Experimental Physics, Institute of Physics (B5), University of Liège, B-4000 Liège Belgium
Abstract:Irradiation in the presence of O2, with near-UV light of five promazine (PZ) derivatives added to erythrocyte ghost membranes, causes covalent cross-linking between proteins as revealed by a progressive decrease in the amounts of proteins separable by electrophoresis after denaturation. The induction of cross-links in the two spectrin subunits is a single-hit process as a function of the irradiation time; relatively the rate constants (in min?1) of the photoreactions were 0.060 with chlorpromazine (CPZ), 0.039 with methoxypromazine (MTPZ), 0.031 with PZ, 0.029 with triflupromazine (TFPZ) and 0.006 with acepromazine (ACPZ).A main photochemical intermediate implicated in the spectrin aggregation seems to be the cation radical of the PZ derivatives. Indeed, (i) the chemically generated cation radicals can induce the reaction in the dark; (ii) the photoaggregation is regularly reduced upon addition of increasing concentrations of NaN3; (iii) NaN3 similarly affects the amount of cross-links induced by the isolated cation radicals. Hydroxyl radicals are also involved in the photocross-linking when the reaction is initiated only by MTPZ and not by the other sensitizers.In the absence of oxygen during irradiation, PZ, MTPZ and ACPZ completely loose their cross-linking activities whereas CPZ and TFPZ remain as efficient as in the presence of oxygen.
Keywords:Membrane proteins - Photosensitization - Near-UV irradiation - Phenothiazine - Promazine  ACPZ  acepromazine  CPZ  chlorpromazine  MTPZ  methoxypromazine  PZ  promazine  SDS  sodium dodecyl sulphate  TFPZ  triflupromazine
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