Light/dark labeling differences in chloroplast membrane polypeptides associated with chloroplast coupling factor 0

The fluorogenic reagent fluorescamine has been used to determine the labeling patterns of Type C spinach chloroplast membrane polypeptides. Membrane polypeptides labeled with fluorescamine were detected by scanning high resolution sodium dodecyl sulfate polyacrylamide gradient slab gels for fluorescence emission.Three membrane polypeptides show a decrease in the extent of labeling when chloroplast membranes are labeled in the light compared to when they are labeled in the dark. These polypeptides have apparent molecular weights of 32 000, 23 000 and 15 000.The decrease in labeling observed in the light is abolished or reduced by treatments which inactivate the light-generated transmembrane pH gradient. CF₁-depleted chloroplasts show neither a light-activated pH gradient nor a light/dark difference in labeling of these three polypeptides. Both a light-activated pH gradient and light/dark differences in labeling are observed in CF₁-depleted chloroplasts which have been treated with N,N′-dicyclohexylcarbodiimide.The same ammonium sulfate fractions of a 2% sodium cholate extract, which are believed to be enriched in the membrane-bound sector of the chloroplast ATPase (CF_o) are also found to be enriched in the 32 000, 23 000 and 15 000 molecular weight polypeptides. The three polypeptides are believed to be components of CF_o, and the light/dark labeling differences may indicate conformational changes within CF_o. Such conformational changes may reflect a mechanism which couples light-generated proton gradients to ATP synthesis.