Purified subunit δ of chloroplast coupling factor CF1 reconstitutes photophosphorylation in partially CF1‐depleted membranes
- 1 February 1988
- journal article
- research article
- Published by Wiley in European Journal of Biochemistry
- Vol. 172 (1) , 213-218
- https://doi.org/10.1111/j.1432-1033.1988.tb13875.x
Abstract
The ATP synthase of chloroplasts consists of the proton channel, CF0, and the catalytic part, CF1, which carries nucleotide-binding sites on subunits .alpha. and .beta.. The poorly understood interaction between CF0 and the catalytic sites on CF1 is mediated by the smaller subunits .gamma., .delta. and .epsilon. of CF1. We investigated the ability of purified .delta. to block proton leakage through CF0 channels after their exposure by removal of the CF1 counterpart. Thylakoids were partially depleted of CF1 by EDTA treatment. This increased their proton permeability and thereby reduced the rate of photophosphorylation. Subunit .delta. was isolated and purified by FPLC [Englebrecht, S. and Junge, W. (1987) FEBS Lett. 219, 321-325]. Addition of .delta. to EDTA-treated thylakoids reconstituted high rates of phenazine-methosulfate-mediated photophosphorylation. Since .delta. does not interact with nucleotides by itself, the reconstitution was due to a reduction of the proton leakage through open CF0 channels. The molar ratio of purified .delta. over exposed CF0, which started to elicit this effect, was 3:1. However, if .delta. was added together with purified CF1 lacking .delta., in a 1:1 molar ratio, the relative amount over exposed CF0 was as low as 0.06. This corroborated our previous conclusion [Lill, H., Engelbrecht, S., Schonknecht, G. and Junge, W. (1986) Eur. J. Biochem. 160, 627-634] that only a very small fraction of exposed CF0 was actually proton-conducting but with a very high unit conductance. DV1 including .delta. was apparently rebound preferentially to open CF0 channels. Although the ability of .delta. to control proton conduction through CF0 was evident, it remains to be established whether .delta. acts as a gated proton valve or as a conformational transducer in the integral CF0CF1 ATPase.This publication has 44 references indexed in Scilit:
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