The ∈ subunit of the chloroplast ATP synthase of Pisum sativum

Abstract

In contrast to the well-characterized spinach ( Spinacea oleracea) chloroplast ATP synthase (CF1–CFo), the properties of the chloroplast ATP synthase from pea (Pisum sativum ) have not been as intensively studied. Preliminary data 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 was also higher than that of spinach CF1 in the absence of activating treatments. These differences could result from the different regulatory properties of the pea ∈ or γ subunit or both. The pea ∈ subunit was less effective in binding to or inhibiting the ATPase activity of pea o r spinach CF1 deficient in ∈ (CF1-∈). Spinach ∈ inhibited the ATPase activity of pea CF1-∈ at lower concentrations than pea ∈. The gene encoding the pea ∈ subunit was cloned and over-expressed. Recombinant pea ∈ did not restore low proton permeability to spinach thylakoid membranes reconstitituted with spinach CF1-∈, although pea ∈ was effective when tested with pea thylakoids reconstitituted with pea CF1-∈. These results confirm earlier suggestions that the C-terminal region of ∈ is important in ∈-CF1 and ∈-CFo interactions.