The proton-ATPase complex

The proton-ATPase complex, first purified by Pick and Racker [54], was reported to contain nine different subunits, four of which may belong to the membrane sector. Later studies in our laboratory detected only three subunits in the... 

Subunit structure and function of the proton ATPase complex... 

Fig. 12.1. Relative sizes of mitochondrial and chloroplast chromosomes and location of protein structural genes. The figure was constructed from published data [5,15,17,22,26-28]. The structural genes are marked by wide sections. Black areas code for proteins. White areas are introns. 0x1, OxII and OxIII are subunits I, II and III of cytochrome c oxidase. Cyt b, cytochrome b. Fo and Fo, are subunits 6 and 9 of the proton ATPase complex. In the chloroplast chromosome the arrows indicate the transcription direction and the size of the transcripts. CF,a, CFj/8, CFjc and CFoIII are subunits a, /S, t and III of the chloroplast proton ATPase complex [30]. PSII5], PSII44, and PSII34 are subunits of photosystem II reaction center with the corresponding molecular weights of 51000, 44000 and 34000. PSI70 is subunit I of photosystem I reaction center. Cyt /is cytochrome/ cyt is cytochrome b and b -flV is subunit IV of cytochrome b(,-f complex.

ATP synthesis and hydrolysis in chloroplasts are catalyzed by the proton -ATPase complex. The turnover capacity of the enzyme seeirssto be highly regulated. Photophosphorylating and ATPase activities were higher in chloroplasts rapidly prepared from preilluminated leaves (Morita "el al", 1982 Vallejos "et al", 1983). 

CONSERVATION AND ORGANIZATION OF SUBUNITS OF THE CHLOROPLAST PROTON ATPase COMPLEX... 

Proton ATPase complex was incubated with DMS (O) or DIG (A) after reconstitution into liposomes, at 0°G. At the time indicated in the figure, samples were taken to measure ATP-Pi exchange activity. The activity of the untreated complex was 60 n mol/mg protein/min. 

Figure 4. The interaction of cross-linked proton ATPase complex with antibodies.

Proton ATPase complex from spinach chloroplasts was treated with DMS or DIG and run on gel as described in Fig 2, transfered to nitrocellulose paper and treated with antibodies and I protein A as described under "Materials and Methods". The antibodies used were raised against subunits c<.(A), Ti(C), f(D), (E), 1(F) and 11(G) of spinach chloroplasts and (B) of E. coli membranes. 1-untreated complex, 2- complex cross-linked with DMS and 3- complex treated with Die. 

Figure 6. A model of the arrangement of the different subunits of the chloroplast proton ATPase complex.

The effect of iodosobenzoate is reversible (Vallejos, Andreo, 1976). Apparently the situation is similar in light-chloroplasts where two accessible sulfhydryl groups may be blocked by M-ethylmaleimide (Vallejos et al , 1983). However, the proton ATPase is active in this Ccise but not in broken chloroplasts subject to illumination. Thus, activation in vivo of the proton ATPase may involve reduction of the second disulfide bond of the y subunit or may required other changes in the complex. 

Figure 7 Mixld for iron (Fe) deficiency induced changes in root physiology and rhizo-sphere chemistry associated with Fc acquisition in strategy I plants. (Modified froin Ref. 1.) A. Stimulation of proton extru.sion by enhanced activity of the plasnialemma ATPase —> Felll solubilization in the rhizospherc. B. Enhanced exudation of reductanls and chela-tors (carhoxylates. phenolics) mediated by diffusion or anion channels Pe solubilization by Fein complexation and Felll reduction. C. Enhanced activity of plasma membrane (PM)-bound Felll reductase further stimulated by rhizosphere acidificalion (A). Reduction of FolII chelates, liberation of Fell. D. Uptake of Fell by a PM-bound Fell transporter.

F-ATPases (including the H+- or Na+-translocating subfamilies F-type, V-type and A-type ATPase) are found in eukaryotic mitochondria and chloroplasts, in bacteria and in Archaea. As multi-subunit complexes with three to 13 dissimilar subunits, they are embedded in the membrane and involved in primary energy conversion. Although extensively studied at the molecular level, the F-ATPases will not be discussed here in detail, since their main function is not the uptake of nutrients but the synthesis of ATP ( ATP synthase ) [127-130]. For example, synthesis of ATP is mediated by bacterial F-type ATPases when protons flow through the complex down the proton electrochemical gradient. Operating in the opposite direction, the ATPases pump 3 4 H+ and/or 3Na+ out of the cell per ATP hydrolysed. 

Transporting ATP synthase [EC 3.6.1.34] in plants, also referred to as chloroplast ATPase and CFiCFo-ATPase, catalyzes the hydrolysis of ATP to produce ADP and orthophosphate. When coupled with proton transport the reverse reaction results in the synthesis of ATP by this multisubunit complex. CFi, isolated from the rest of the membrane-bound complex, retains the ATPase activity but not the proton-translocating activity. 

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