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12‐(9‐Anthroyl)‐stearic acid and atebrin as fluorescence probes for energetic states of chloroplasts
Author(s) -
Vandermeulen David L.
Publication year - 1974
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(74)80842-2
Subject(s) - citation , library science , chemistry , biophysics , polymer science , computer science , biology
Ever since the introduction of the chemiosmotic hypothesis [l] for the coupling of phosphorylation to electron flow, the role of the two major components (pH gradient, ApH, and membrane potential, a$) of the total electrochemical energy gradient utilized for ATP synthesis has been actively investigated in several systems [2-91. The importance of both the proton gradient [6,7] and the membrane potential [8,9] aspects of the total proton motive force has been demonstrated in chloroplast systems. In this report, a comparison of the effects of antibiotics (valinomycin, gramicidin, nigericin) on the light and dark responses of the fluorescence probes 12(9-anthroyl) stearate (AS) and atebrin illustrates their potential usefulness in the investigation of the relation of the membrane potential to the energy conservation mechanism. It is believed that these probes may provide valuable information regarding an energetic membrane state involved in the coupling of phosphorylation to photosynthetic electron flow, including any participating membrane conformational changes. The experiments reported in this paper demonstrate a light-indticed, phenazine methylsulfate (PMS) catalyzed, biphasic increase in AS fluorescence inhibited by uncouplers of phosphorylation e.g. NH4 Cl and suppressed by phosphorylating conditions (ADP, Pi, Mg’+). Valinomycin (in the presence of K+) in the dark produced a diffusion-potential-induced stimulation of AS fluorescence which may be correlated to a stimulation of ATP synthesis by a membrane potential [9]. The effect of valinomycin on the light response of the 186 fluorescence probe atebrin, reported here, which monitors some function of the ‘energized state’ in chloroplasts [lo- 131, could also be correlated with the effects of valinomycin on AS fluorescence. Thus, the fluorescent probe, AS, used here for the first time with chloroplasts, is suggested to report an ‘energy state’ of the thylakoid membrane.