Abstract
Rabbit antiserum raised against the isolated native epsilon subunit of the chloroplast coupling factor 1 activated the ATPase activity of coupling factor 1 in solution by removing the epsilon subunit. Incubation of thylakoid membranes with the antiserum in the dark had no effect on photophosphorylation or on the dithiothreitol-induced Mg2+-ATPase activity. Incubation with the antiserum during illumination, however, strongly inhibited both activities and caused the membranes to become leaky to protons. The results indicate that the formation of a proton gradient across the thylakoid membrane induces a change in conformation of the epsilon subunit of the ATP synthase such that it becomes susceptible to attack and removal by the antibodies. This change may be a part of the mechanism that results in energy-dependent activation of the ATP synthase.
Highlights
Rabbit antiserum raised against the isolated native t reasonable t o conclude that overcoming t inhibition is a part subunit of the chloroplast coupling factor 1 activated of the energy-dependent activatioonf the ATP synthase
Incubation of CF, with t antiserum caused a marked stimulation of the Ca2+-ATPase activity of the enzyme (Fig. 1)
The light dependence for the antiserum effect may result of a proton gradient across the thylakoid membrane
Summary
Incubation of CF, with t antiserum caused a marked stimulation of the Ca2+-ATPase activity of the enzyme (Fig. 1). Treatment of thylakoid membranes with the antiserum in at room temperature in 0.5 ml of reaction mixture containing 50 mM the dark had littleffect on CFlactivity. One ml of Ca2+-ATPase reaction mixture containing 50 mM Tris-HC1 (pH 8), mM ATP, and 5 mM CaClzwas added to each sample and Pi determined after 5min of incubation at 37 "C. E Antibody Effectson CF, mination (Table I) This is consistent with the uncoupling precipitated by centrifugation.Themembranes were effect of the antiserum sincea proton gradient isrequired for subjected to a 10-min light treatment (Table 11). Incubation with the antiserum in the dark had no effect on Addition of fresh antiserum during the light treatment results either activity (Table I). ATP hydrolyzed per hour permg of chlorophyll was obtained results in the removal of the tightly bound t subunit from after treating thylakoids equivalent to 25 pg of chlorophyll soluble CF1. This indicates that the antiserum t subunit which are notnormally exposed inthe dark inactive had removed the t subunit from about15% of the membrane- state of CF1become exposed during illumination
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