THE REGULATION OF LIGHT-DEPENDENT PROTON EFFLUX FROM CHLOROPLAST THYLAKOIDS

MARILYN SULLIVAN ABBOTT, Purdue University

Abstract

The work presented in this study contributes to the characterization of the phenomenon of light-dependent proton efflux from chloroplast thylakoids. Two aspects are addressed: (1) the relationship between light-dependent proton efflux and the energized state of the membrane; and (2) the identity of the membrane component(s) which regulate(s) this proton flux. The first order rate constant of light-dependent proton efflux (k(,0)) generated by whole chain or partial (PS I or PS II) electron transport reactions was measured as a function of the electron transport rate. At a given electron transfer rate, the k(,0) resulting from the whole chain reaction was double that produced by either partial reaction. The rate constant k(,0) was found not to be related to the size of the transmembrane electrical potential. However, k(,0) may be regulated by either the rate of proton uptake accompanying light-induced electron transport or by the transmembrane pH gradient which results. The light-induced exchange of tightly-bound adenine nucleotides (AdN) was utilized as an indicator of the activation state of the coupling factor (CF(,1)). The % AdN-depleted CF(,1) and the rate constant k(,0) were found to respond identically to all conditions of light intensity, pH and energy transfer inhibition tested. The conclusion from these experiments is that the rate constant of light-dependent proton efflux is determined by the steady-state number of AdN-depleted CF(,1)'s. These results are consistent with a model in which the energy of the protonmotive force causes a change in the conformation of the coupling factor. This conformational change leads to both release of previously bound AdN and an increase in proton permeability through the CF(,1).

Degree

Ph.D.

Subject Area

Biology

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