pH Changes in the Cytoplasm of the Blue-Green Alga Anacystis nidulans Caused by Light-dependent Proton Flux into the Thylakoid Space

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Abstract
The pH in the cytoplasmic and thylakoid spaces of the blue-green alga A. nidulans was determined in the light and in the dark by uptake of 5,5-dimethyloxazolidine-2,4-dione and methylamine into the sucrose-impermeable 3H-H2O space, as measured by Si layer filtering centrifugation. Illumination causes an alkalinization in the cytoplasm which is accompanied by an acidification in the thylakoid space, reflecting light-dependent proton transport across the thylakoid membrane. Under light conditions a pH gradient of approximately 2.8 between the cytoplasmic and thylakoid spaces was measured that can be abolished almost completely by addition of the uncoupler, 3-chlorocarbonyl cyanide phenylhydrazone. The pH in the cytoplasm is independent of the pH in the medium.

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