Protons, the thylakoid membrane, and the chloroplast ATP synthase

Journal Article · Sun Jan 01 04:00:00 EST 1989 · Annals of the New York Academy of Sciences; (USA)

DOI:https://doi.org/10.1111/j.1749-6632.1989.tb25164.x· OSTI ID:6871791

Junge, W ^[1]

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1. Universitaet Osnabrueck, Osnabrueck (Germany, F.R.)

According to the chemiosmotic theory, proton pumps and ATP synthases are coupled by lateral proton flow through aqueous phases. Three long-standing challenges to this concept were examined in the light of experiments carried out with thylakoids: (1) Nearest neighbor interaction between pumps and ATP synthases. Considering the large distances between photosystem II and CFoCF1, in stacked thylakoids this is a priori absent. (2) Enhanced proton diffusion along the surface of the membrane. This could not be substantiated for the outer side of the thylakoid membrane. Even for the interface between pure lipid and water, two laboratories have reported the absence of enhanced diffusion. (3) Localized proton ducts in the membrane. Intramembrane domains that can transiently trap protons do exist in thylakoid membranes, but because of their limited storage capacity for protons, they probably do not matter for photophosphorylation under continuous light. Seemingly in favor of localized proton ducts is the failure of a supposedly permeant buffer to enhance the onset lag of photophosphorylation. However, it was found that failure of some buffers and the ability of others in this respect were correlated with their failure/ability to quench pH transients in the thylakoid lumen, as predicted by the chemiosmotic theory. It was shown that the chemiosmotic concept is a fair approximation, even for narrow aqueous phases, as in stacked thylakoids. These are approximately isopotential, and protons are taken in by the ATP synthase straight from the lumen. The molecular mechanism by which F0F1 ATPases couple proton flow to ATP synthesis is still unknown. The threefold structural symmetry of the headpiece that, probably, finds a corollary in the channel portion of these enzymes appeals to the common wisdom that structural symmetry causes functional symmetry.

• OSTI ID: 6871791
• Journal Information: Annals of the New York Academy of Sciences; (USA), Journal Name: Annals of the New York Academy of Sciences; (USA) Vol. 574; ISSN 0077-8923; ISSN ANYAA
• Country of Publication: United States
• Language: English

Related Subjects

550200* -- Biochemistry
59 BASIC BIOLOGICAL SCIENCES
ACID ANHYDRASES
ATP-ASE
BARYONS
BIOCHEMICAL REACTION KINETICS
CELL CONSTITUENTS
CHLOROPLASTS
ELEMENTARY PARTICLES
ENZYMES
FERMIONS
HADRONS
HYDROLASES
KINETICS
MEMBRANE PROTEINS
MEMBRANE TRANSPORT
MEMBRANES
MOLECULAR BIOLOGY
NUCLEONS
ORGANIC COMPOUNDS
PHOSPHOHYDROLASES
PHOTOSYNTHETIC MEMBRANES
PHOTOSYNTHETIC REACTION CENTERS
PROTEINS
PROTONS
REACTION KINETICS