ATP synthetase complex

As an example of an asymmetric membrane integrated protein, the ATP synthetase complex (ATPase from Rhodospirillum Rubrum) was incorporated in liposomes of the polymerizable sulfolipid (22)24). The protein consists of a hydrophobic membrane integrated part (F0) and a water soluble moiety (Ft) carrying the catalytic site of the enzyme. The isolated ATP synthetase complex is almost completely inactive. Activity is substantially increased in the presence of a variety of amphiphiles, such as natural phospholipids and detergents. The presence of a bilayer structure is not a necessary condition for enhanced activity. Using soybean lecithin or diacetylenic sulfolipid (22) the maximal enzymatic activity is obtained at 500 lipid molecules/enzyme molecule. With soybean lecithin, the ATPase activity is increased 8-fold compared to a 5-fold increase in the presence of (22). There is a remarkable difference in ATPase activity depending on the liposome preparation technique (Fig. 41). If ATPase is incorporated in-... 

Figure 11.7 Electron (e ) transport along the inner mitochondrial membrane resulting in the pumping of protons (P) out of the mitochondrial matrix. Protons are shuttled back into the matrix through the ATP synthetase complex where ATP is generated. Sites of toxicant action are indicated.

Pantothenic acid has a central role in energy-yielding metabolism as the functional moiety of coenzyme A (CoA), in the biosynthesis of fatty acids as the prosthetic group of acyl carrier protein, and through its role in CoA in the mitochondrial elongation of fatty acids the biosynthesis of steroids, porphyrins, and acetylcholine and other acyl transfer reactions, including postsynthetic acylation of proteins. Perhaps 4% of all known enzymes utilize CoA derivatives. CoA is also bound by disulfide links to protein cysteine residues in sporulating bacteria, where it may be involved with heat resistance of the spores, and in mitochondrial proteins, where it seems to be involved in the assembly of active cytochrome c oxidase and ATP synthetase complexes. 

Experimental synthesis of ATP at the octane/water interface was carried out [11, 12, 20]. The proton flow through the ATP-synthetase complex from octane to water was provided by creating an excess (relative to equilibrium) concentration of undissociated (or Lewis) acid in the octane phase (Fig. 37). This was achieved in three ways by direct addition of add-pentachlorphenol to octane, by the action of NADH-ferricyanidreductase of the respiratory chain of submitochondrial particles, and also through the action of the H -pump of bacteriorhodopsin sheets from Halobacterium halobium. 

Figure 1.1. Simplified scheme showing electron transport in a portion of a chloroplast thylakoid membrane. Electrons flow from water via an oxygen-evolving complex (OEC) to photosystem II (PS2), pheophytin (PHEO), plastquinone (PQ), plastocyanin (PC) to photosystem I (PSI). Aq, Chlorophyll FeS, iron-sulfur centres FD, ferredoxin. Phosphorylation is catalyzed by proton transport through a transmembrane proton channel (CFq) to the ATP-synthetase complex (CF,).

By observing changes in nucleotides that alter substrate specificity, researchers have identified nucleotide positions that are involved in discrimination by the amino-acyl-tRNA synthetases. These nucleotide positions seem to be concentrated in the amino acid arm and the anticodon arm, including the nucleotides of the anticodon itself, but are also located in other parts of the tRNA molecule. Determination of the crystal structures of aminoacyl-tRNA synthetases complexed with their cognate tRNAs and ATP has added a great deal to our understanding of these interactions (Fig. 27-17). 

The rate limiting step in fatty acid synthesis is catalyzed by acetyl-CoA carboxylase to produce malonyl-CoA at the expense of one ATP.31 Malonate and acetate are transferred from CoA to acyl carrier protein in the cytosolic fatty acid synthetase complex, where chain extension leads to the production of palmitate. Palmitate can then be transferred back to CoA, and the chain can be extended two carbons at a time through the action of a fatty acid elongase system located in the endoplasmic reticulum. The >-hydroxylation that produces the >-hydroxyacids of the acylceramides is thought to be mediated by a cytochrome p450 just when the fatty acid is long enough to span the endoplasmic reticular membrane. 

Rould MA, Perona JJ, S011 D, Steitz TA (1989) Structure of E. coli glutaminyl-tRNA synthetase complexed with tRNAoln and ATP at 2.8 A resolution implications for tRNA discrimination. Science 246 1135-1142... 

F26BP, fructose-2,6-bisphosphate FA, fatty acid FAD, fatty acid desaturase FADH2/FAD, reduced/oxidized flavin adenine dinucleotide F -ATPase, ATP synthetase F complex FGF, fibroblast growth factor FGF-RTK, fibroblast growth factor receptor tyrosine kinase Fmet, formylmethionine FMNH2/FMN, reduced/oxidized flavin mononucleotide... 

Figure 6-5. Energetics and directionality of the coupling between electron flow and ATP formation in chloroplasts, emphasizing the role played by H+ (see also Fig. 5-19). The02 evolution from H20 and the electron flow via plastoquinones (PQ) and the cytochrome complex (Cyt b6f) lead to H+ accumulation in the lumen of a thylakoid. This H+ can moveback out through a hydrophobic channel (CF0) and another protein factor (CF, which together comprise the ATP synthetase, leading to ATP formation.

The membrane-bound ATP synthetase couples phosphorylation to a proton gradient [90] which is generated by the cyclic electron transfer system (Fig. 3). This system includes the RC, a UQ pool [91], a Cyt bic complex [92,93], and a specialized Cyt c (E j = -fO.34 V) for transferring electrons to the oxidized primary donor (P-870 or P-970 ) of the RC. In some bacteria such as Chromatiurn vi-nosum and Rhodopseudomonas viridis this specialized Cyt c is bound to the RC in the membrane [93,94], whereas in other bacteria such as Rb. sphaeroides and Rhodospirillum rubrum this cytochrome is a periplasmic protein (Cyt C2) that binds to the membrane-bound RC [90]. 

Most of the thylakoid proteins are organized into four intrinsic protein complexes PS II complex, Cyt b/f complex, PS I complex and ATP synthetase (Fig. 1). The electron transport complexes are linked by mobile electron transport carriers, plastoquinone, plastocyanin and ferredoxin (see Chapter 10). Furthermore, chloroplasts that possess Chi b have the major light-harvesting Chi a/h-proteins of PS II (LHC II) that may represent over 50% of the thylakoid protein [13], as well... 

ATP synthetase was the first thylakoid complex to be positively localized by Miller and Staehelin [51] who demonstrated unequivocally by antibody labelling studies that CF, was present only in non-appressed membranes. The bulky CF, component that protrudes some 9-14 nm into the stromal matrix would prevent ATP synthetase being located in the appressed membrane regions that approach one another to = 3 nm under illumination [6]. 

The biosynthesis of ATP involves the flow of both electrons (e ) and protons (H ) in the respiratory chain to form ATP by the process known as oxidative phosphorylation. The respiratory chain comprises four structures known as complex I, complex II, complex III and complex IV and a mushroom-shaped structure (ATP synthetase alias Fq/Fi or complex V) that synthesises ATP from ADP and inorganic phosphate (Pi). We will consider the flow of electrons and protons (i) first from complex I, and (ii) from complex II. 

This complex consists of the stem of the mushroom Fq (fraction sensitive to oligomycin) that contains the proton chaimel, and the bulbous part ATP synthetase (or Fi, the 1st fraction to be discovered). The proton current flows through the proton channel and drives a molecular motor that causes ADP and Pi to react to form ATP. 

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