An overview of ATP synthesis and its key components
To make a long story short, the primary function of ATP synthase in most organisms is ATP synthesis. Hence the name. However, in some cases the reverse reaction, i.e. transmembrane proton pumpingpowered by ATP hydrolysis is more important. A typical example: anaerobic bacteria produce ATP byfermentation, and ATP synthase uses ATP to generate protonmotive force necessary for ion transportand flagella motility.
Many bacteria can live both from fermentation and respiration or photosynthesis. In such case ATP synthasefunctions in both ways.
An important issue is to control ATP-driven proton pumping activity of ATP synthase in order to avoid wasteful ATP hydrolysis under conditions when no protonmotive force can be generated (e.g. leakydamaged membrane, uncoupler present, etc.). In such case ATP hydrolysis becomes a problem,because it can quickly exchaust the intecellular ATP pool. To avoid this situation,all ATP synthases are equipped with regulatory mechanisms that suppress the ATPaseactivity if no protonmotive force is present. The degree of ATP hydrolysis inhibitiondepend on the organism. In plants (in chloroplasts), where it is necessary to preserveATP pool through the whole night, the inhibition is very strong: the enzyme hardly has anyATPase activity. In contrast, in anaerobic bacteria where ATP synhase is the maingenerator of protonmotive force, such inhibition is very weak. Mitochondrial ATP synthase is somewhereinbetween.
because the production of ATP in mitochondria is ..
Cancer-specific metabolism, which is closelyassociated with tumorigenicity, cancer aggressive progression andinherent or acquired therapeutic resistance, is an attractivetarget for cancer therapy. The role of PKM2 in glycolysis and theproliferation of cancer cells has been revealed, and has beendemonstrated to balance the production of biomolecular buildingblocks and the generation of pyruvate and ATP. Consequently, thereare two therapeutic strategies for targeting PKM2. The first isinhibitors that block the catalytic activity of PKM2, and thesecond is activators that induce tetramerization of PKM2 toincrease glycolysis.
The conclusion from the example above is:
The energy provided by ATP hydrolysis is not fixed (as well as theenergy necessary to synthesize ATP). Infirst approximation it depends on the concentrations of ADP, ATP, Piand on the pH. This energy increases logarithmically upon decrease inADP and Pi concentration and upon increase in ATP or H+ concentration (= decreases linearly with increase in pH). The graphs below illustrate this point, showingchange in the upon the change in theconcentrationof one reactant ( axis),assuming that the concentrations of other reactants are kept constantat values used in the example above (red dots indicate the calculated in this example).
To close up this section, I would like to note that although thethermodynamics of the ATP synthesis described here might seem rathercomplex, it is actually much more complex. One point neglected here wasthe different ADP and ATP protonation states (), the other is that the actual substrates in the reactioncatalyzed by ATP synthase are not pure nucleotides, but their magnesiumcomplexes. However, as the magnesium concentration in the living cellis relatively high and the pH is usually above 7.2, so the descriptiongiven is still applicable for thermodynamic estimates.
The driving force for the synthesis of ATP is the H + gradient, ..
Oligomycin is the inhibitor that gave the name "FO" to the membrane-embedded portion of ATP synthase. The subscript letter "O" in FO(not zero!) comes from Oligomycin sensitivity of this hydrophobicphosphorylation Factor in mitochondria.
Oligomycin binds on theinterface of subunit and -ring oligomer and blocks the rotary proton translocation in FO. If the enzyme is well-coupled, the activity of F1is also blocked. Because of the latter phenomenon, a subunit of mitochondrial F1-portionthat connects F1 with FO was named Oligomycin-Sensitivity Conferring Protein (OSCP).This subunit is essential for good coupling between F1 and FO and makes the ATPase activity of F1 sensitive to FO inhibitor oligomycin, hence the name.
Oligomycin is specific for mitochondrial ATP synthase and in micromolar concentrationseffectively blocks proton transport through FO. This inhibitor also works in some bacterial enzymes that show highsimilarity to mitochondrial ATP synthase, e.g. enzyme from purple bacterium . But ATP synthase from chloroplasts and from most bacteria (including )has low sensitivity to oligomycin.
It should also be noted that oligomycin in high concentrations also affects the activity of mitochondrial F1.
Animations for translation in protein synthesis
DCCD (abbreviation for Dicyclohexylcarbodiimide; also known as DCC, as N,N'-dicyclohexylcarbodiimide, as Bis(cyclohexyl)carbodiimide, and as 1,3-dicyclohexylcarbodiimide) is a small organic molecule thatcan covalently modify protonated carboxyl groups. When added to ATP synthase at pH above 8, DCCD almost exclusively reacts with the carboxyl group of the conserved acidic amino acid residue of subunit (that is why subunit is sometimes called "DCCD-binding protein"). that has elevated pK and can therefore be protonated at such a high pH. Modification of the carboxyl group in a single -subunit is enough to renderthe whole -ring oligomer inactive. Because DCCD covalently binds to -subunit,this inhibition is irreversible.
The carboxyl group of the conserved amino acid residue in subunit -subunit is present inall ATP synthases known so far. So DCCD is a universal inhibitor that can FO function in bacterial, mitochondrial and chloroplast enzymes. Moreover, V- and A-type proton-transporting ATPasesare also sensitive to DCCD for the same reason. Sodium-transporting ATP synthases are also effectively inhibited by DCCD.
At lower pH (1 and inactivates it. So this compound canbe considered as an inhibitor of both FO and F1. However, inhibition of FOis highly specific, well-defined, and requires much lower DCCD concentration so usually thisinhibitor is used as FO-specific.