The epsilon subunit of the chloroplast ATP synthase of Pisum sativum

In contrast to the well-characterized spinach (Spinacea oleracea) chloropla st ATP synthase (CF1-CFo), the properties of the chloroplast ATP synthase f rom pea (Pisum sativum) have not been as intensively studied. Preliminary d ata suggested that the regulatory properties of the two enzymes differ. In the absence of activating treatments the ATPase activity of pea thylakoids in the dark was higher than that in spinach thylakoids. When assayed in the presence of sulfite, the MgATPase activity of pea thylakoids was inhibited to a maximum of 67% by tentoxin, indicating that the dark ATPase activity is in part catalyzed by CF1-CFo. The ATPase activity of purified pea CF1 wa s also higher than that of spinach CF1 in the absence of activating treatme nts. These differences could result from the different regulatory propertie s of the pea epsilon or gamma subunit or bath. The pea epsilon subunit was less effective in binding to or inhibiting the ATPase activity of pea or sp inach CF1 deficient in epsilon (CF1-epsilon). Spinach epsilon inhibited the ATPase activity of pea CF1-epsilon at lower concentrations than pea epsilo n. The gene encoding the pea epsilon subunit was cloned and over-expressed. Recombinant pea epsilon did not restore low proton permeability to spinach thylakoid membranes reconstitituted with spinach CF1-epsilon, although pea epsilon was effective when tested with pea thylakoids reconstitituted with pea CF1-epsilon. These results confirm earlier suggestions that the C-term inal region of epsilon is important in epsilon-CF1 and epsilon-CFo interact ions.