Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P20020 (adenosine triphosphatase)
 3,299 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A study was made of the enzyme content of the isolated cell walls and of a plasma-membrane preparation obtained by centrifugation after enzymic digestion of the cell walls of baker's yeast. The isolated cell walls showed no hexokinase, alkaline phosphatase, esterase or NADH oxidase activity. It was concluded that these enzymes exist only in the interior of the cell. Further, only a negligible activity of deamidase was detectable in the cell walls. Noticeable amounts of saccharase, phosphatases hydrolysing p-nitrophenyl phosphate, ATP, ADP, thiamin pyrophosphate and PP(i), with optimum activity at pH3-4, and an activity of Mg(2+)-dependent adenosine triphosphatase at neutral pH, were found in the isolated cell walls. During enzymic digestion, the other activities appearing in the cell walls were mostly released into the medium, but the bulk of the Mg(2+)-dependent adenosine triphosphatase remained in the plasma-membrane preparation. Accordingly, it may be assumed that the enzymes released into the medium during digestion are located in the cell wall outside the plasma membrane, whereas the Mg(2+)-dependent adenosine triphosphatase is an enzyme of the plasma membrane. This enzyme differs from the phosphatases with pH optima in the range pH3-4 with regard to location, pH optimum, substrate specificity and different requirement of activators.
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PMID:The enzymic composition of the isolated cell wall and plasma membrane of baker's yeast. 431 24

Experiments with the aerotolerant anaerobe Streptococcus lactis provide the opportunity for determining the proton motive force (Deltap) in dividing cells. The two components of Deltap, DeltaPsi (the transmembrane potential) and DeltapH (the chemical gradient of H(+)), were determined by the accumulation of radiolabeled tetraphenylphosphonium (TPP(+)) and benzoate ions. The DeltaPsi was calibrated with the K(+) diffusion potential in starved, valinomycin-treated cells. With resting, glycolyzing cells, the Deltap was measured also by the accumulation of the non-metabolizable sugar thiomethyl-beta-galactoside (TMG). In resting cells the Deltap, calculated either by adding DeltaPsi and ZDeltapH or from the levels of TMG, was relatively constant between pH 5 to 7, decreasing from 160 to 150 mV and decreasing further to 100 mV at pH 8.0. With the TPP(+) probe for DeltaPsi, we confirmed our previous finding that the K(+) ions dissipate DeltaPsi and increase DeltapH, whereas Na(+) ions have little effect on DeltaPsi and no effect on DeltapH. [(3)H]TPP(+) and [(14)C]benzoate were added during exponential phase to S. lactis cells growing at pH 5 to 7 at 28 degrees C in a defined medium with glucose as energy source. As with resting cells, the DeltapH and DeltaPsi were dependent on the pH of the medium. At pH 5.1, the DeltapH was equivalent to 60 mV (alkaline inside) and decreased to 25 mV at pH 6.8. The DeltaPsi increased from 83 mV (negative inside) at pH 5.1 to 108 mV at pH 6.8. The Deltap, therefore, was fairly constant between pH 5 and 7, decreasing from 143 to 133 mV. The values for Deltap in growing cells, just as in resting cells, are consistent with a system in which the net efflux of H(+) ions is effected by a membrane-bound adenosine triphosphatase and glycolytically generated adenosine triphosphate. The data suggest that in both growing and resting cells the pH of the medium and its K(+) concentration are the two principal factors that determine the relative contribution of DeltapH and DeltaPsi to the proton motive force.
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PMID:Proton motive force during growth of Streptococcus lactis cells. 677 26