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The Coupling of Electron Flow to ATP Synthesis in Pea and Maize Mesophyll Chloroplasts ^1,2

I. INTERACTION OF ADENINE NUCLEOTIDES AND ENERGY TRANSFER INHIBITORS WITH THE COUPLING FACTOR COMPLEX

T. H. Morgan School of Biological Sciences, University of Kentucky, Lexington, Kentucky 40506

The rate of nonphosphorylating electron transport (in the absence of ADP and inorganic phosphate) in well-coupled (ATP/2e^– = 0.9-1.1) maize mesophyll chloroplasts is not modulated by external pH (6.5-8.5), low levels of ADP or ATP, or energy transfer inhibitors, e.g. triphenyltin and Hg²⁺ ions. In contrast nonphosphorylating electron flow in pea chloroplasts is sensitive to alterations in medium pH, and to the presence of adenine nucleotides and energy transfer inhibitors in the assay medium. Although ATP is without effect on the rate of basal electron transport in maize chloroplasts, steady-state proton uptake is stimulated 3- to 5-fold by low levels of ATP. These results suggest that differences may exist in the manner in which the coupling factor complex controls proton efflux from the intrathylakoid space in C₃ and C₄ mesophyll chloroplasts.

¹ This research was supported by National Science Foundation Grant PCM76-17214.

² A preliminary report of this work was presented at the annual meeting of the American Society of Plant Physiologists, Columbus, Ohio, July 1979.