The value of surface charge in the thylakoid membranes of chloroplasts is determined by a number of the free ionogenic groups of integral protein complexes exposed into the water phase and depends on pH and the ionic strength of the medium. The aim of the present work was to estimate a contribution of ionogenic groups of two greatest polypeptide assemblies of the thylakoid membranes of chloroplasts - ATP-synthase and light-harvesting complex of photosystem II (LHCII) - to the total charge value of a thylakoid membrane. Acid-base titration curves of thylakoids, isolated from fresh cut pea leaves and treated to prepare membranes with various amounts of LHCII and the catalytic part of ATP-synthase (factor CF1), were studied. For obtaining thylakoids with various amounts of LHCII, pea plants were grown at high (1200<$E mu> mol <$E roman {m sup -2 s} sup -1>) and low (120<$E mu> mol <$E roman {m sup -2 s} sup -1>) light intensities. The amount of LHCII in plants grown at high light intensity was much lower, than that in plants grown at weak light. A factor CF1 was depleted from the thylakoid surface by the 2 M NaBr treatment. Judging from the titration curves of CF1-depleted thylakoid membranes and the membranes with various amounts of LHCII, the surface proteins of ATP-synthase contain only a negligible number of ionogenic groups with pK 4 - 9 and make no important contribution to the surface charge variation in thylakoids in the physiological pH range. At the same time, the ionogenic groups of LHCII apparently take part in the surface charge formation in thylakoids.

• Подорванов Володимир Вікторович (1960–2020) (біологічні науки)

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