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 language||English (US)|
|Number of pages||7|
|Journal||Journal of Biological Chemistry|
|State||Published - 1992|
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology