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Hepatic endosome fractions contain an ATP-driven proton pump.

ABSTRACT: Endosome fractions were isolated from rat liver homogenates on the basis of the subcellular distribution of circulating ligands, e.g. 125I-asialotransferrin internalized by hepatocytes by a receptor-mediated process. The distribution of endocytosed 125I-asialotransferrin 1-2 min and 15 min after uptake by liver and a monensin-activated Mg2+-dependent ATPase activity coincided on linear gradients of sucrose and Nycodenz. The monensin-activated Mg2+-ATPase was enriched relative to the liver homogenates up to 60-fold in specific activity in the endosome fractions. Contamination of the endosome fractions by lysosomes, endoplasmic reticulum, mitochondria, plasma membranes and Golgi-apparatus components was low. By use of 9-aminoacridine, a probe for pH gradients, the endosome vesicles were shown to acidify on addition of ATP. Acidification was reversed by addition of monensin. The results indicate that endosome fractions contain an ATP-driven proton pump. The ionophore-activated Mg2+-ATPase in combination with the presence of undegraded ligands in the endosome fractions emerge as linked markers for this new subcellular organelle.

SUBMITTER: Saermark T

PROVIDER: S-EPMC1144552 | biostudies-other | 1985 Jan

REPOSITORIES: biostudies-other

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A natural light-driven inward proton pump.

Project description:Light-driven outward H+ pumps are widely distributed in nature, converting sunlight energy into proton motive force. Here we report the characterization of an oppositely directed H+ pump with a similar architecture to outward pumps. A deep-ocean marine bacterium, Parvularcula oceani, contains three rhodopsins, one of which functions as a light-driven inward H+ pump when expressed in Escherichia coli and mouse neural cells. Detailed mechanistic analyses of the purified proteins reveal that small differences in the interactions established at the active centre determine the direction of primary H+ transfer. Outward H+ pumps establish strong electrostatic interactions between the primary H+ donor and the extracellular acceptor. In the inward H+ pump these electrostatic interactions are weaker, inducing a more relaxed chromophore structure that leads to the long-distance transfer of H+ to the cytoplasmic side. These results demonstrate an elaborate molecular design to control the direction of H+ transfers in proteins.

| S-EPMC5118547 | biostudies-literature

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| S-EPMC8387761 | biostudies-literature

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| S-EPMC5462737 | biostudies-literature

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| S-EPMC3711326 | biostudies-literature

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| S-EPMC4657025 | biostudies-literature

Crystallographic structure of xanthorhodopsin, the light-driven proton pump with a dual chromophore.

Project description:Homologous to bacteriorhodopsin and even more to proteorhodopsin, xanthorhodopsin is a light-driven proton pump that, in addition to retinal, contains a noncovalently bound carotenoid with a function of a light-harvesting antenna. We determined the structure of this eubacterial membrane protein-carotenoid complex by X-ray diffraction, to 1.9-A resolution. Although it contains 7 transmembrane helices like bacteriorhodopsin and archaerhodopsin, the structure of xanthorhodopsin is considerably different from the 2 archaeal proteins. The crystallographic model for this rhodopsin introduces structural motifs for proton transfer during the reaction cycle, particularly for proton release, that are dramatically different from those in other retinal-based transmembrane pumps. Further, it contains a histidine-aspartate complex for regulating the pK(a) of the primary proton acceptor not present in archaeal pumps but apparently conserved in eubacterial pumps. In addition to aiding elucidation of a more general proton transfer mechanism for light-driven energy transducers, the structure defines also the geometry of the carotenoid and the retinal. The close approach of the 2 polyenes at their ring ends explains why the efficiency of the excited-state energy transfer is as high as approximately 45%, and the 46 degrees angle between them suggests that the chromophore location is a compromise between optimal capture of light of all polarization angles and excited-state energy transfer.

| S-EPMC2575459 | biostudies-literature

Transcript profiling of Arabidopsis plasma membrane proton pump mutants

2015-04-01 | GSE34202 | GEO

Transcript profiling of Arabidopsis plasma membrane proton pump mutants

Project description:Plasma membrane proton pump maintains proton electrochemical gradient and provides energy to secondary transporters. Arabidopsis mutant plants with reduced proton pump activity grow normal under ideal growth conditions; however their growth are reduced compared with wildtype plants when placed under the conditions that stress on protonmotive force (high external pH or high external potassium). Seedlings of wildtype, aha1, and aha2 mutant plants were grown under ideal growth condition. Total RNA from those seedlings were subjected to transcriptome analyses using Affymetrix Gene Chip.

2015-04-01 | E-GEOD-34202 | biostudies-arrayexpress

36 degrees step size of proton-driven c-ring rotation in FoF1-ATP synthase.

Project description:Synthesis of adenosine triphosphate ATP, the 'biological energy currency', is accomplished by F(o)F(1)-ATP synthase. In the plasma membrane of Escherichia coli, proton-driven rotation of a ring of 10 c subunits in the F(o) motor powers catalysis in the F(1) motor. Although F(1) uses 120 degrees stepping during ATP synthesis, models of F(o) predict either an incremental rotation of c subunits in 36 degrees steps or larger step sizes comprising several fast substeps. Using single-molecule fluorescence resonance energy transfer, we provide the first experimental determination of a 36 degrees sequential stepping mode of the c-ring during ATP synthesis.

| S-EPMC2750017 | biostudies-literature

Association of proton pump inhibitors with the risk of hepatic encephalopathy during hospitalization for liver cirrhosis.

Project description:BackgroundHepatic encephalopathy is associated with altered gut microbiota. Proton pump inhibitors increase the risk of small bowel bacterial overgrowth.ObjectivesThis was a case-control study aimed at exploring the relationship of proton pump inhibitor use with the risk of hepatic encephalopathy during hospitalization in liver cirrhosis.MethodsCase and control groups were defined as cirrhotic patients who developed hepatic encephalopathy during hospitalization and those without hepatic encephalopathy at admission or during hospitalization, respectively. Age, gender, and Child-Pugh score were matched between the groups. Odds ratios with 95% confidence intervals were calculated to express the association of proton pump inhibitors with the risk of hepatic encephalopathy. Four subgroup analyses were performed after excluding patients with acute upper gastrointestinal bleeding, infections, and in-hospital death, and after matching model for end-stage liver disease score.ResultsIn the overall analysis, 128 patients were included in each group of cases and controls. The proportion of proton pump inhibitor use was significantly higher in the case group than the control group (79.7% vs 43%, p?<?0.001). Proton pump inhibitor use (odds ratio?=?3.481, 95% confidence interval: 1.651-7.340, p?=?0.001) was independently associated with the development of hepatic encephalopathy in the multivariate analysis. In the four subgroup analyses, proton pump inhibitor use remained independently associated with the risk of hepatic encephalopathy.ConclusionProton pump inhibitor use might increase the risk of hepatic encephalopathy during hospitalization.

| S-EPMC6169047 | biostudies-literature

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