Osteoclasts resorb bone by first attaching to the bone surface and then secreting protons into an isolated extracellular compartment formed at the cell-bone attachment site. This secretion of protons (local acidification) is required to solubilize bone hydroxyapatite crystals and for activity of bone collagen-degrading acid proteases. However, the large quantity of protons required, 2 mol/mol o...

To purify cytoplasmic and mitochondrial isoenzymes of aspartate aminotransferase (EC 2.6.1.1) from human liver. We used heat treatment, ammonium sulfate precipitation, anion- and cation-exchange chromatography, affinity chromatography, and isoelectric focusing. Final preparations of the isoenzymes were homogeneous, with specific activities of 198 and 208 kU/g for the cytoplasmic and the mitocho...

Acidic media trigger cytoplasmic urease activity of the unique human gastric pathogen Helicobacter pylori. Deletion of ureI prevents this activation of cytoplasmic urease that is essential for bacterial acid resistance. UreI is an inner membrane protein with six transmembrane segments as shown by in vitro transcription/translation and membrane separation. Expression of UreI in Xenopus oocytes r...

The response of maize (Zea mays L.) and Spartina anglica root tips to exposure to sodium chloride concentrations in the range 0 to 500 mM was investigated using 23Na and 31P nuclear magnetic resonance spectroscopy (NMR). Changes in the chemical shift of the pH-dependent 31P-NMR signals from the cytoplasmic and vacuolar orthophosphate pools were correlated with the uptake of sodium, and after al...

The influenza M2 protein forms an acid-activated tetrameric proton channel important for the virus lifecycle. Residue His37 in the transmembrane domain is responsible for channel activation and proton selectivity. While the structure and dynamics of His37 have been well studied in TM peptide constructs, it has not been investigated in the presence of the full cytoplasmic domain, which increases...

The ameliorating effect of nitrate on the acidification of the cytoplasm during short-term anoxia was investigated in maize (Zea mays) root segments. Seedlings were grown in the presence or absence of nitrate, and changes in the cytoplasmic and vacuolar pH in response to the imposition of anoxia were measured by in vivo (31)P nuclear magnetic resonance spectroscopy. Soluble ions and metabolites...

We previously showed that liposomes composed of dioleoylphosphatidyl-ethanolamine and palmitoyl-homocysteine (8:2) are highly fusion competent when exposed to an acidic environment of pH less than 6.5. (Connor, J., M. B. Yatvin, and L. Huang, 1984, Proc. Natl. Acad. Sci. USA. 81:1715-1718). Palmitoyl anti-H2Kk was incorporated into these pH-sensitive liposomes by a modified reserve-phase evapor...