Fi ATP synthase

FIGURE 5.21 The X-ray structure of the Fi-ATP synthase from bovine heart mitochondria. The a, P, and y subunits are in red, yellow, and blue respectively. The inset (bottom left) shows the orientation of the subunits in this view. The bar is 20 A long. From Abrahams, Leslie, Latter, Walker, 1994.)... 

Nucleotide binding conformational changes of Fi ATP synthase complex. See text for details. [Reproduced with permission from Y. Zhou, T. M. Duncan and R. L. Crass Subunit rotation in Escherichia coli FqFi-ATP synthase during oxidative phosphorylation. Proc. Natl. Acad. Sci. 94, 10583 (1997). 1997 by the National Academy of Sciences.]... 

Fig. 9. (A) Schematic representation of photophosphoryiation in a reconstituted iiposome containing photosystem-l reaction centers and CFo Fi ATP synthase, both purified from spinach chloroplasts, using PMS as the electron donor/acoeptor system. (B) Rate of photophosphoryiation as a function of light intensity (left) and time dependence of reconstituted photophosphoryiation (right). Figure source (B) Hauska, Samoray, Orlich and Nelson (1980) Reconstitution of photosynthetic energy conservation. II. Photophosphoryiation in liposomes containing photosystem-l reaction center and chloroplast coupling-factor complex. Eur J Biochem 111 540.

In Fig. 15 (D), the imaginary membrane vesicle is replaced either by an actual chloroplast thylakoid-membrane vesicle containing ATP synthase, as shown in the example of Bauermeister, Schloddder and Graber" or by a liposome reconstituted with isolated CFo Fi-ATP synthase. In the actual experiment, two platinum electrodes each 5 cm in area were spaced 2 mm apart and filled with a chloroplast suspension. The cuvette containing the chloroplast suspension and the electrodes was then thermostated at 4 °C and kept from light. 

With the development of the theory of the binding-change mechanism and the investigations that have provided evidence for the rotary motion ofthe y-subunit, the y s subcomplex, or even the c-subunit oligomer of Fq, anew model that is more detailed than that shown earlier in Fig. 6 for the Fo F -ATP synthase has evolved. Before we present the current model for the Fq Fi-ATP synthase, we will briefly review information obtained by NMR studies for the structure of the smaller 8 and e subunits of F, and also some structure information obtained by X-ray crystallography in the case ofthe e-subunit. The structure ofthe Fo-subunits a, b and c will also be described. 

Subunit a is the largest ofthe three (molecular mass, 30.3 kDa) and highly hydrophobic. Subunit a of EcFq shows a strong amino-acid homology to its counterpart in the Fq Fi-ATP synthase of other species, particularly in the regions near the C-terminus where the residues essential for proton translocation are located. Fig. 38 (A) shows how subunit a is folded across the membrane with either five or six transmembrane helices, resulting in exposure ofthe N-terminus to the cytoplasm and the C-terminus to the periplasm in proposed five-helix model or with both termini exposed to cytoplasm in proposed 6-helix model. 

Figure 15.19 FI ATP synthase as a rotary engine driving the synthesis of ATP. 

ATP synthase contains a membrane-spanning domain, sometimes known as the Fo subunit, and a knobby protmsion that extends into the matrix, the Fi subunit. The mechanism of ATP synthase is not what one would naively predict. The Fi ATP synthase subunit can perform its ligase function (making ATP from ADP and phosphate) without proton flow into the matrix however, release of the ATP requires flow of protons through the membrane. 

The proton concentration gradient produced by all these processes is used in Fq.Fi ATP synthase complexes. The proton flow generated by the proton motive force rotates the Fq subunit, which drives ATP synthesis in the Fi subunit. ... 

Khananshvili D and Gromet-Elhanan Z (1982a) Isolation and purification of an active y subunit of the Fq Fi-ATP synthase from chromatophore membranes of Rhodospirillum rubrum, J. Biol. Chem. 257, 11377-11383. 

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