A PROBLEM IN MEASURING TRANSMEMBRANE PH GRADIENTS IN THE PRESENCE OF LIPOPHILIC AMINES

The possibility of using lipophilic penetrating amines for measuring t ransmembrane pH gradient has been examined. With pea chloroplasts it w as found that light-induced uptake df neutral red, in contrast to imid azole, only poorly reflects the formation of the concentration gradien t of neutral red cations and only slightly depends on the proton gradi ent under stationary illumination. Cations of lipophilic amines (neutr al red, 9-aminoacridine, and tetracaine), in contrast to hydrophilic i midazole and ammonium, are able to displace each other from binding si tes on the thylakoid membrane. This makes it impossible to use lipophi lic amines even for qualitative estimation of the proton gradient if a nother penetrating amine is present in the reaction medium.