Modifications of the γ subunit of chloroplast coupling factor 1 alter interactions with the inhibitory ε subunit

P. Soteropoulos, K. H. Suss, R. E. McCarty

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55 Scopus citations


The treatment of chloroplast coupling factor 1 (CF1) with dithiothreitol or with trypsin modifies the γ subunit. Reduction of the γ subunit disulfide bond in CF1 in solution with dithiothreitol enhances the dissociation of ε (Duhe, R. J., and Selman, B. R. (1990) Biochim. Biophys. Acta 1017, 70-78). The Ca2+-ATPase activity of either oxidized or reduced CF1 increases as the enzyme is diluted. Added ε subunit inhibits the Ca2+-ATPase activity of both forms of the diluted CF1, suggesting that ε dissociation is the cause of activation by dilution. Half-maximal activation occurred at much higher concentrations of the reduced CF1, indicating that reduction decreases the affinity for ε about 20-fold. Immunoblotting techniques show that there is only one ε subunit/CF1 in intact chloroplasts, in thylakoid membranes, and in solution. No ε is released from CF1 in thylakoids under conditions of ATP synthesis. The γ subunit of CF1 in illuminated thylakoids is specifically cleaved by trypsin. CF1 purified from thylakoids treated with trypsin in the light is deficient in ε subunit, and has a high rate of ATP hydrolysis. Added ε neither inhibits the ATPase activity of, nor binds tightly to the cleaved enzyme.

Original languageEnglish (US)
Pages (from-to)10348-10354
Number of pages7
JournalJournal of Biological Chemistry
Issue number15
StatePublished - 1992
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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