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| Content Provider | World Health Organization (WHO)-Global Index Medicus |
|---|---|
| Author | Melandri, B. Andrea D'alessandro, Manuela |
| Description | Author Affiliation: D'Alessandro M ( Department of Biology, Laboratory of Biochemistry and Biophysics, University of Bologna, Via Irnerio 42, 40126 Bologna, Italy.) |
| Abstract | In the ATP synthases of Escherichia coli ADP and phosphate exert an apparent regulatory role on the efficiency of proton transport coupled to the hydrolysis of ATP. Both molecules induce clearly biphasic effects on hydrolysis and proton transfer. At intermediate concentrations (∼ 0.5–1 µM and higher) ADP inhibits hydrolysis and proton transfer; a quantitative analysis of the fluxes however proves that the coupling efficiency remains constant in this concentration range. On the other hand at nanomolar concentrations of ADP (a level obtainable only using an enzymatic ATP regenerating system) the efficiency of proton transport drops progressively, while the rate of hydrolysis remains high. Phosphate, at concentrations ≥ 0.1 mM, inhibits hydrolysis only if ADP is present at sufficiently high concentrations, keeping the coupling efficiency constant. At lower ADP levels phosphate is, however, necessary for an efficiently coupled catalytic cycle. We present a model for a catalytic cycle of ATP hydrolysis uncoupled from the transport of protons. The model is based on the available structures of bovine and yeast F $_{1}$ and on the known binding affinities for ADP and P $_{i}$ of the catalytic sites in their different functional states. The binding site related to the inhibitory effects of P $_{i}$ (in association with ADP) is identified as the α $_{HC}$ β $_{HC}$ site, the pre-release site for the hydrolysis products. We suggest, moreover, that the high affinity site, associated with the operation of an efficient proton transport, could coincide with a conformational state intermediate between the α $_{TP}$ β $_{TP}$ and the α $_{DP}$ β $_{DP}$ (similar to the transition state of the hydrolysis/synthesis reaction) that does not strongly bind the ligands and can exchange them rather freely with the external medium. The emptying of this site can lead to an unproductive hydrolysis cycle that occurs without a net rotation of the central stalk and, consequently, does not translocate protons. |
| ISSN | 00063002 |
| Journal | Biochimica et Biophysica Acta (BBA) - Reviews on Cancer |
| Issue Number | 6-7 |
| Volume Number | 1797 |
| Language | English |
| Publisher | Elsevier |
| Publisher Date | 2010-06-01 |
| Publisher Place | Netherlands |
| Access Restriction | Open |
| Subject Keyword | Adenosine Triphosphate Metabolism Proton-Translocating ATPases Chemistry Adenosine Diphosphate Animals Catalytic Domain Hydrolysis In Vitro Techniques Liposomes Models, Biological Phosphates Protons Biochemistry |
| Content Type | Text |
| Resource Type | Article |
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