Photosynthesis | The Heliobacteria

Gregory S. Orf , Kevin Eastward. Redding , in Encyclopedia of Biological Chemistry (3rd Edition), 2021

ATP synthase

The ATP synthase of Hbt. modesticaldum has been purified and biochemically characterized (Yang et al., 2015). The composition of the enzyme was typical of F1Fo ATP synthases: F1-αthreeβ3γδε Fo-abc9–12. (The size of the Fo-c ring was not adamant.) The ATPase activity of the complex was latent only could exist activated by treatment with some detergents. Interestingly, in contrast to the chloroplast FaneFo ATP synthase, ATPase activity of the heliobacterial enzyme was inhibited, rather than activated, past detachment of the F1 head.

Read full chapter

URL:

https://www.sciencedirect.com/scientific discipline/article/pii/B9780128194607002206

Respiratory Chain and ATP Synthase

David K. Whitehouse , ... Anthony Fifty. Moore , in Reference Module in Biomedical Sciences, 2019

The ATP Synthase

The ATP synthase (or F oneF0 ATPase and also referred to as complex V) uses the free energy of an electrochemical gradient of protons (or sodium ions) generated by the respiratory chain to synthesize ATP. The ATP synthases comprise a very big grouping of highly conserved enzymes that are found in the bacterial cytoplasmic membranes, the thylakoid membranes of chloroplasts, and the inner membranes of mitochondria. Nigh members of the group use H+ every bit the coupling ion (the Propionigenium modestum enzyme is an example of the few ATP synthases that can utilize Na+ as the physiological coupling ion).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128012383957325

Citric Acrid Cycle, Electron Transport Chain, and Oxidative Phosphorylation

John West. Pelley PhD , in Elsevier's Integrated Biochemistry, 2007

Proton Pumping and ATP Synthesis

Complex I, complex Iii, and complex IV pump several protons into the intermembrane infinite for every pair of electrons that they ship to O2. A sufficient number of protons are pumped to maintain a 10:one concentration gradient (one pH unit) between the intermembrane space and the matrix.

ATP synthase complex (F oFone-ATP synthase). This complex allows protons to flow dorsum into the matrix and uses the complimentary energy change from this process to synthesize ATP from ADP and inorganic phosphate (Pi). It is located in knob-shaped structures embedded in the cristae (invaginations of the inner mitochondrial membrane) and extending into matrix.

•

The Fo protein (the "o" in Fo refers to its sensitivity to oligomycin, a toxicant that blocks the menses of protons) extends through the inner mitochondrial membrane and serves as the proton channel between the intermembrane space and the matrix.

The ATP synthase (Fone-ATPase) is attached to the Fo poly peptide on the inside of the matrix. ATP synthase uses the protons flowing into the matrix to bind ADP and Pi and release ATP. The F1-ATPase is named by the contrary reaction information technology catalyzes when it is isolated from mitochondria and thus uncoupled from the proton slope.

KEY POINTS ABOUT THE ELECTRON Ship Chain

▪

The electron transport chain is located in the mitochondrial inner membrane and contains several unlike kinds of electron carriers: flavin mononucleotide, atomic number 26-sulfur proteins, coenzyme Q, heme-containing cytochromes, and copper ions.

▪

Three big multiprotein complexes serve as proton pumps by harnessing the energy from electron menstruum through the ETC to oxygen; in turn, the chemiosmotic free energy in the proton gradient that is created by the pumps is coupled to the synthesis of ATP by the ATP synthase complex.

▪

ATP regulates its own synthesis and the flow of electrons through respiratory command; if ATP synthesis slows downwards, electron send slows down and vice versa.

▪

Cytosolic NADH cannot laissez passer through the mitochondrial membrane, so it shuttles its electrons through the glycerol phosphate shuttle and the malate-aspartate shuttle.

▪

ATP and ADP are transported in commutation for each other by the ATP/ADP translocase.

Read full affiliate

URL:

https://www.sciencedirect.com/science/commodity/pii/B9780323034104500134

Cellular Bioenergetics

David G. Nicholls , Stuart J. Ferguson , in Bioenergetics (Fourth Edition), 2013

9.13 The ATP Synthase Inhibitor Protein IFone

Further reading: Campanella et al. (2009), Faccenda and Campanella (2012)

The ATP synthase is freely reversible, and its direction depends on the thermodynamic balance betwixt Δ p and the matrix ΔG p. Damage to the electron transport chain, increased proton leakage, or severe hypoxia can lower Δp such that the ATP synthase reverses in the cell and starts to hydrolyse cytoplasmic ATP generated past glycolysis. Experimentally, this reversal tin can be detected as a decrease in Δψm upon addition of the ATP synthase inhibitor oligomycin (see Effigy 12.two). Nether these conditions, glycolysis is called on to service not only the entire ATP demand of the cell just also the synthase reversal. One result of this is that cells may deplete their cytoplasmic ATP to the extent that glycolysis and fatty acrid oxidation, both of which require ATP, cannot proceed and the cell dies. This condition is also approached in many published experiments in which protonophores are added to cells, in which case mitochondrial ATP hydrolysis can be extremely rapid, being no longer limited past the depression inner membrane proton permeability. Although the ATP depletion tin can exist alleviated in vitro by the addition of oligomycin, a more subtle physiological mechanism exists in many cells, mediated by the 10-kDa inhibitor protein (IFone; Section 7.vi).

IFane can bind to the Fone-ATP synthase under atmospheric condition of acidic matrix pH, partially inhibiting its catalytic activity. At the molecular level, studies with Escherichia coli ATP synthase suggest that IF1 acts every bit a 'ratchet' preventing reversal of the enzyme (Department seven.6). Because an acidic matrix is normally only seen nether hypoxic conditions, when the electron transport pathway is inhibited, or in the presence of a protonophore, this essentially means that IFi tin can inhibit ATP synthase reversal but is without result on ATP synthesis (when the matrix is alkaline). The inhibition is not complete only depends on the ratio of IFone to the ATP synthase complex and may play an of import part in limiting ATP depletion in hypoxia (Figure 9.eighteen). Neurons mostly possess higher ratios of IF1 to F1 than astrocytes, with the issue that electron chain inhibition causes a more profound depolarisation of the sometime while slowing cytoplasmic ATP depletion.

Figure 9.18. The inhibitor protein IF1.

Schematic of the predicted time courses of ATP depletion (magenta) and ∆ψm (red) following ischaemia in a cell possessing maximal IFone activity (solid lines) and lacking IFane (dashed lines). The presence of the inhibitor protein prolongs the fourth dimension for which the cell retains ATP, merely at the price of a rapid mitochondrial depolarisation.

 Information adapted from Campanella et al. (2009).

Read full affiliate

URL:

https://world wide web.sciencedirect.com/science/article/pii/B9780123884251000099

ANTI-ATP SYNTHASE β-CHAIN AUTOANTIBODIES

LUCA MUSANTE , ... GIAN MARCO GHIGGERI , in Autoantibodies (2d Edition), 2007

Disease Association

Circulating ASA of the IgM course accept been showtime described in seven patients with nephrotic syndrome; some of these patients also presented a combination of ASA and anti-actin (three cases) and anti-nuclear (three cases) autoantibodies. Therefore, ASA represents the almost reproducible mark of autoimmunity in these patients merely a clear clinical and pathogenetic human relationship with the disease cannot be divers. Overall, patients with circulating ASA could not be readily differentiated from other patients with primary NS with respect to clinical and pathologic characteristics. As detailed in Table 67.1, all patients of our series had an early onset of proteinuria (between 1 and 8 years) and had strict resistance or dependence to steroids; 6 had been treated with cyclosporine and only iv were sensitive. Sensitivity to cyclosporine was associated with good long-term issue in all cases. High plasma levels of IgM was a abiding finding in all patients and in one reached the relevant limit of i.000 mg%, in the absence of monoclonal band. The histological background was focal segmental glomerulosclerosis (FSGS) in 3 children while 2 presented diffuse mesangial proliferation with IgM degradation and i had an unspecific pattern. Three patients developed during the follow-upward positiveness for antinuclear antibodies (ANA).

TABLE 67.i. Clinical Features of 7 Patients with Nephrotic Syndrome who Presented Anti-podocyte Antibodies

Type of Antibody Age Age at Onset Serum IgM mg% Parameter ANA Drug Steroids Sensitivity Cyclosporin Histology IF ESRF TX
IgM-anti Actin and ATP Synthase
Patient one (LD) 17.iii 8.3 1.2 pos 1:360 resistant resistant FSGS IgM no
Patient 2 (DE) eight.7 i.4 400 pos one:160 dependent sensitive Mes Prol IgM no
Patient 3 (LS) 7 3.05 neg dependent sensitive Mes Prol IgM no
IgM-anti ATP Synthase
Patient 4 (BB) 25 fourteen nd neg resistant not utilized unspecific nd yes yeah
Patient 5 (AL) 19 fourteen nd neg resistant resistant FSGS nd yep yes
Patient half-dozen (ED) 7 2 200 pos i:80 dependent sensitive nd nd no
Patient vii (VD) nine.6 2.i 174 neg dependent sensitive FSGS IgM no

Abbreviations: IF, immunofluorescence; ESRF, finish stage renal failure; FSGS, focal segmental glomerulosclerosis; TX, renal transplant.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780444527639500718

THE ATP SYNTHASE

In Bioenergetics 2, 1992

7.7 NON-THERMODYNAMIC REGULATION OF THE ATP SYNTHASE

The ATP synthases from various sources are regulated in several ways. The mitochondrial enzyme has an additional subunit known as the inhibitor protein. The binding of one molecule to a β-subunit is sufficient to block ATP hydrolysis in the absenteeism of a Δ p (Harris and Das, 1991). The inhibition is removed in the presence of a Δp, and thus the inhibitor poly peptide may act to foreclose unwanted ATP hydrolysis past mitochondria under weather condition such as anoxia when the ATP synthase would otherwise reverse. The regulation in leaner is less well understood. In the case of P. denitrificans and many other organisms in which respiration and hence oxidative phosphorylation is obligatory, ATP hydrolysis and an ATP–Pi substitution reaction is very feeble in the absence or presence of a Δp. It is not known if these leaner possess inhibitor proteins.

In thylakoids an essential requirement is to avert ATP hydrolysis in the nighttime. In the calorie-free, activation of the ATP synthase follows exposure of a disulphide bridge in the γ-subunit and its reduction past a thioredoxin which in turn is reduced by ferredoxin. The latter is reduced by the activity of photosystem I (Section 6.4.3). In the dark, ATP synthase relaxes back into an inactive state because reduced ferredoxin and thioredoxin are no longer formed and the disulphide span reforms under the more oxidizing weather condition. A dimer of a mercaptohistidine compound may exist the direct oxidant for the cysteine thiol groups that reform the disulphide bridge (Selman-Reimer et al., 1991).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780125181242500126

The Chemiosmotic Proton Excursion in Isolated Organelles

David G. Nicholls , Stuart J. Ferguson , in Bioenergetics (Fourth Edition), 2013

four.6 ATP Synthase Reversal

The ATP synthase is reversible and is only constrained to run in the direction of net ATP synthesis by the continual regeneration of Δ p and the utilise of ATP by the cell. If the respiratory chain is inhibited and ATP is supplied to the mitochondrion, or if sufficient Ca2+ is added to depress Δp below that for thermodynamic equilibrium with the ATP synthase reaction, the enzyme complex functions every bit an ATPase, generating a Δp comparable to that produced by the respiratory concatenation. The proton circuit generated by ATP hydrolysis must exist completed past a means of proton re-entry into the matrix. Proton translocators therefore accelerate the rate of ATP hydrolysis, just equally they accelerate the charge per unit of respiration; this is the 'uncoupler-stimulated ATPase activity,' which is of particular importance in the cellular context, when mitochondrial dysfunction can cause ATP synthase reversal and drain glycolytically generated ATP. In some circumstances, an 'inhibitor poly peptide,' IF1, can limit this reversal ( Sections 7.7 and 9.xiii Section 7.vii Department 9.13 ).

The classic means of discriminating whether a mitochondrial free energy-dependent process is driven direct by Δp or indirectly via ATP is to investigate the sensitivity of the procedure to the ATP synthase inhibitor oligomycin. A Δp-driven consequence would be insensitive to oligomycin when the potential was generated past respiration, just it would exist sensitive when Δp was produced past ATP hydrolysis. The converse would be truthful of an ATP-dependent event. If Δp or Δψ is existence monitored, mitochondria (isolated or in situ), which are net generators of ATP, will hyperpolarise (i.e., Δp will increment) on addition of oligomycin, whereas those whose Δp is supported by ATP hydrolysis will depolarise. This 'null-point' analysis is a uncomplicated way of monitoring mitochondrial role within cells (Figure 12.2).

Under physiological conditions, the mitochondrial ATP synthase will not normally be called upon to act as a proton-translocating ATPase, except perchance during periods of anoxia when glycolytic ATP could be utilised to maintain the mitochondrial Δp. However, some bacteria, such as Streptococcus faecalis when grown on glucose, lack a functional respiratory chain and rely entirely on hydrolysis of glycolytic ATP to generate a Δp across their membrane and enable them to transport metabolites.

Read full chapter

URL:

https://www.sciencedirect.com/science/commodity/pii/B978012388425100004X

THE CHEMIOSMOTIC PROTON Circuit

In Bioenergetics ii, 1992

4.11 REVERSED ELECTRON TRANSFER AND THE PROTON CIRCUIT DRIVEN Past ATP HYDROLYSIS

The ATP synthase is reversible and is merely constrained to run in the direction of net ATP synthesis by the continual regeneration of Δ p and the use of ATP by the prison cell. If the respiratory chain is inhibited and ATP is supplied to the mitochondrion, the ATP synthase functions equally an ATPase, generating a Δp comparable to that produced by the respiratory concatenation. The proton excursion generated past ATP hydrolysis must exist completed by a ways of proton re-entry into the matrix. Proton translocators therefore accelerate the rate of ATP hydrolysis, simply as they accelerate the rate of respiration; this is the 'uncoupler-stimulated ATPase activity'.

The classic means of discriminating whether a mitochondrial energy-dependent procedure is driven direct by Δp or indirectly via ATP is to investigate the sensitivity of the process to the ATP synthase inhibitor oligomycin. A Δp-driven event would be insensitive to oligomycin when the potential was generated past respiration, but sensitive when Δp was produced by ATP hydrolysis. The converse would be true of an ATP-dependent upshot.

The near equilibrium in state 4 betwixt Δp and the redox spans of complexes I and 3 suggests that conditions could be devised in which these segments of the respiratory concatenation could be induced to run backwards, driven past the inward flux of protons. It should be noted that this does not utilise to complex 4, which is essentially irreversible. Reversed electron transfer may be induced in two means, either through generating a Δp by ATP hydrolysis, or by using the flow of electrons from succinate or cyt c to Otwo to reverse electron transfer through complexes I or I and III respectively (Fig. four.19). Such a menstruum of electrons, east.thou. from succinate, involves the majority of the electron flux passing to Otwo and thereby generating Δp whilst a minority is driven energetically uphill to reduce NAD+ at the expense of Δp.

Effigy 4.nineteen. Reversed electron transfer in the mitochondrial respiratory chain.

Schematic response of submitochondrial particles incubated in the presence of NAD+. In (a), a Δp is generated by succinate oxidation. Δp then drives complex I in reverse, causing NAD+ reduction, i.e. succinate acts as both donor of electrons for reversed electron transfer and as substrate for complexes III and IV. In (b) complex 3 is inhibited by antimycin A and the Δp is generated by ATP hydrolysis. Succinate merely donates electrons for reversed electron transfer through complex I.

Under physiological conditions the mitochondrial ATP synthase will not normally exist called upon to deed as a proton-translocating ATPase, except maybe during periods of anoxia when glycolytic ATP could be utilized to maintain the mitochondrial Δp. Even so, some bacteria, such as Streptococcus faecalis when grown on glucose, lack a functional respiratory chain and rely entirely upon hydrolysis of glycolytic ATP to generate a Δp across their membrane and enable them to send metabolites. Reversed electron ship driven by Δp generated through respiration is an essential process in some bacterial species (see Affiliate 5).

Read full chapter

URL:

https://www.sciencedirect.com/scientific discipline/article/pii/B9780125181242500096

ATP23 Peptidase

Claudia Wilmes , Thomas Langer , in Handbook of Proteolytic Enzymes (Tertiary Edition), 2013

Processing and Assembly of Atp6

The FiFO ATP synthase converts the proton gradient across the mitochondrial inner membrane into chemical energy in the form of ATP [iv]. It consists of mitochondrial besides as nuclear encoded subunits, the latter being synthesized in the cytosol and imported into mitochondria via conserved protein translocases [5]. The FO subunit Atp6 is mitochondrial encoded and integrated into the F1FO ATP synthase at a belatedly step of the assembly process [vi]. While it has been recognized already in 1988 that Atp6 in Southward. cerevisiae is synthesized equally a forerunner protein with an N-terminal extension of 10 amino acid residues that are cleaved off [7], only recently Atp23 has been identified equally the peptidase that mediates North-terminal Atp6 processing [1,2]. Replacement of the catalytically active glutamate residue at position 168 (Glu168Gln) within the metallopeptidase domain of Atp23 inactivates the peptidase and results in the aggregating of the precursor form of Atp6. Surprisingly, Δatp23 cells expressing Atp23E168Q remain respiration competent indicating that Atp6 maturation is not required for its assembly into the F1FO ATP synthase. In dissimilarity, deletion of ATP23 impaired the respiratory competence of the yeast cells. Atp6 accumulates at drastically reduced steady land levels in these cells and the associates of the FiFO ATP synthase is impaired [1,ii]. Co-immunoprecipitation experiments revealed direct binding of Atp23 to newly synthesized, mature Atp6 [2]. Therefore, Atp23 exerts dual activities during the biogenesis of the F1FO ATP synthase in yeast mitochondria: it mediates the processing of newly synthesized Atp6 and ensures the assembly of mature Atp6 into the FO-moiety of the FoneFO ATP synthase. Similar-sized assembly intermediates accumulate in the absence of Atp23 or of the assembly factor Atp10, which is localized in the matrix space and facilitates the interaction of Atp6 with the Atp9 band circuitous within the FO-particle [7,viii]. Overexpression of Atp23 was constitute to be an effective suppressor of an atp10 zip mutant [one]. These findings suggest a sequential binding of newly synthesized Atp6 to Atp10 and to Atp23, which mediates Atp6 maturation in the intermembrane space and its association with Atp9 ring complexes.

Read total chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123822192003835

Defense Bespeak Peptides

Yube Yamaguchi , ... Alisa Huffaker , in Handbook of Biologically Agile Peptides (Second Edition), 2013

Distribution of the mRNA/peptide

The chloroplastic ATP synthase from which inceptin is derived is ubiquitous and constitutively present in foliar and other chloroplast-rich tissues. Because inceptins are the products of a domain particular to chloroplastic ATP synthases, they are not generated from other ATPase proteins. Because of the cleavage of inceptin from the γ-subunit past insect digestive enzymes, it seems probable that the production of bioactive peptide is limited to occasions of biotic interaction. Information technology is non known whether endogenous establish proteolysis activities ever result in inceptin production in the absence of herbivory. Although inceptins act as defence force elicitors but in Vigna and Phaseoulus species, the corresponding domain of the cATPase γ-subunit is widely conserved across plant species, and inceptin peptides are detected in oral secretions of armyworms that have fed on maize and tobacco too equally legumes. 28

Read total chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123850959000026