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ATP synthesis at physiological nucleotide concentrations.

ABSTRACT: Synthesis of ATP by the F1F0 ATP synthase in mitochondria and most bacteria is energized by the proton motive force (pmf) established and maintained by respiratory chain enzymes. Conversely, in the presence of ATP and in the absence of a pmf, the enzyme works as an ATP-driven proton pump. Here, we investigate how high concentrations of ATP affect the enzymatic activity of the F1F0 ATP synthase under high pmf conditions, which is the typical situation in mitochondria or growing bacteria. Using the ATP analogue adenosine 5'-O-(1-thiotriphosphate) (ATP?S), we have developed a modified luminescence-based assay to measure ATP synthesis in the presence of millimolar ATP concentrations, replacing an assay using radioactive nucleotides. In inverted membrane vesicles of E. coli, we found that under saturating pmf conditions, ATP synthesis was reduced to ~10% at 5?mM ATP?S. This reduction was reversed by ADP, but not Pi, indicating that the ATP/ADP ratio controls the ATP synthesis rate. Our data suggests that the ATP/ADP ratio ~30 in growing E. coli limits the ATP synthesis rate to ~20% of the maximal rate possible at the applied pmf and that the rate reduction occurs via product inhibition rather than an increased ATP hydrolysis rate.

SUBMITTER: Meyrat A

PROVIDER: S-EPMC6395684 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature

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ATP synthesis at physiological nucleotide concentrations.

Meyrat Axel A von Ballmoos Christoph C

Scientific reports 20190228 1

Synthesis of ATP by the F1F0 ATP synthase in mitochondria and most bacteria is energized by the proton motive force (pmf) established and maintained by respiratory chain enzymes. Conversely, in the presence of ATP and in the absence of a pmf, the enzyme works as an ATP-driven proton pump. Here, we investigate how high concentrations of ATP affect the enzymatic activity of the F1F0 ATP synthase under high pmf conditions, which is the typical situation i ...[more]

PMID: 30816129

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Project description:Vitamin D may have anti-tumorigenic actions by influencing the gene expression profile of target tissues, which possess vitamin D receptors. We used a more physiological in vitro model, represented by short-term culture of breast cancer tissue slices, to study the transcriptional effects of a near physiological concentration of calcitriol. Methods. Breast cancer fragments were sliced and maintained in culture for 24 hours in the presence or absence (control) of calcitriol 0.5nM or 100nM (called physiological or supra-physiological concentrations). Five and 16 samples were included in a test or validation group and gene expression was analyzed by microarray (using SAM paired analysis) or qPCR, respectively. Results. Nine genes were regulated by calcitriol 0.5nM including CYP24A1, DPP4, EFTUD1 (FDR£0.01), which were up-modulated. However, using a less stringent FDR value (0.25) 61 genes were differentially expressed. Among the down-regulated transcripts were members of the MHC class II complex (HLA-DPA1, HLA-DQA1, HLA-DQA2, HLA-DQB1, HLA-DRA, HLA-DRB1, HLA-DRB3) and IgG binding (FCGR2A, FCGR2B, FCGR2C). There was an enrichment of genes presenting transcription factor binding sites for vitamin D, among the up-regulated genes and for interferon regulatory factor IRF1, among the down-regulated genes. Analyzing calcitriol supra-physiological effects, a more impressive transcriptional modulation was identified and 136 and 60 genes (FDR 0.1) were more and less expressed in treated samples. Up-regulated genes were involved in vitamin metabolic process, regulation of leukocyte-mediated immunity and positive regulation of alpha-beta T cell activation. Many of the induced genes were already reported as vitamin D responsive genes, including CD14, which was also up-regulated in another set of 16 samples. Genes modulated by both calcitriol concentrations were CYP24A1, DPP4, CA2 (these three in both sets of samples), EFTUD1, TKTL1, KCNK3. Conclusion. Small increments in calcitriol concentration, within the physiological range, for a relatively short period of time may exert transcriptional effects in breast cancer samples. Further studies employing physiological concentrations of vitamin D for longer periods of time may help to elucidate the hormone effects in breast cancer treatment and prevention.

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ATP synthesis at physiological nucleotide concentrations.

Publications

ATP synthesis at physiological nucleotide concentrations.

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