Distribution of individual cytoplasmic pH values in a population of the yeast<i>Saccharomyces cerevisiae</i>

Cimprich, Petr; Slavík, Jan

doi:10.1111/j.1574-6968.1995.tb07727.x

Cited by 33 publications

(4 citation statements)

References 15 publications

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“…Because marked fluctuations of the pH often occur in biological systems, pH homeostasis has to compensate for changes in the environment. The intracellular pH value of yeast is kept at a value of between pH 5 and 6 (32). Optimum pH for activity of yeast chorismate mutase between 5.0 and 6.5 coincides with the findings for intracellular pH values and the cellular biochemistry here seems to be well adapted to intracellular conditions.…”

Section: Discussionsupporting

confidence: 80%

A glutamate residue in the catalytic center of the yeast chorismate mutase restricts enzyme activity to acidic conditions

Schnappauf

Sträter²,

Lipscomb³

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

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Chorismate mutase acts at the first branchpoint of aromatic amino acid biosynthesis and catalyzes the conversion of chorismate to prephenate. Comparison of the x-ray structures of allosteric chorismate mutase from the yeast Saccharomyces cerevisiae with Escherichia coli chorismate mutase͞prephenate dehydratase suggested conserved active sites between both enzymes. We have replaced all critical amino acid residues, Arg-16, Arg-157, Lys-168, Glu-198, Thr-242, and Glu-246, of yeast chorismate mutase by aliphatic amino acid residues. The resulting enzymes exhibit the necessity of these residues for catalytic function and provide evidence of their localization at the active site. Unlike some bacterial enzymes, yeast chorismate mutase has highest activity at acidic pH values. Replacement of Glu-246 in the yeast chorismate mutase by glutamine changes the pH optimum for activity of the enzyme from a narrow to a broad pH range. These data suggest that Glu-246 in the catalytic center must be protonated for maximum catalysis and restricts optimal activity of the enzyme to low pH.

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Section: Discussionsupporting

confidence: 80%

A glutamate residue in the catalytic center of the yeast chorismate mutase restricts enzyme activity to acidic conditions

Schnappauf

Sträter²,

Lipscomb³

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

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“…This pH requirement for RhAG-mediated complementation correlates with the predicted plasma membrane proton gradient (Table I). The intracellular pH (pH i ) in yeast is correlated with the pH of the medium (pH o ) (19). At acidic pH o 4.3-5.3, the pH i is relatively alkaline , so the direction of the proton gradient is inward.…”

Section: Discussionmentioning

confidence: 99%

Mechanism of Genetic Complementation of Ammonium Transport in Yeast by Human Erythrocyte Rh-associated Glycoprotein

Westhoff

Siegel

Burd

et al. 2004

Journal of Biological Chemistry

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؉ -H ؉ -exchanger. To further delineate the functional properties of RhAG, in this study we have expressed RhAG in both a Saccharomyces cerevisiae ammonium-transport mutant (mep1⌬ mep2⌬ mep3⌬) and a wild-type strain. RhAG was able to complement the transport mutant, with complementation strictly pH-dependent, requiring pH 6.2-6.5. RhAG also conferred resistance to methylamine (MA), a toxic analog of ammonium, and expression in wild-type cells revealed that resistance was correlated with efflux of MA. RhAG-mediated resistance was pH-dependent, being optimal at acid pH. The opposite pH dependence of ammonium complementation (uptake) and MA resistance (efflux) is consistent with bidirectional movement of substrate counter to the direction of the proton gradient. This report clarifies and expands previous observations of RhAG-mediated transport in yeast and supports the hypothesis that ammonium transport is coupled to the H ؉ gradient and that RhAG functions as a NH 4 ؉ /H ؉ exchanger.

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“…Early 31 P NMR studies indicated that yeast intracellular pH was not affected by the external pH conditions or the presence of NH 4 ϩ (41). However, several subsequent studies found that the intracellular pH of yeast followed the external pH when the extracellular medium was either strongly buffered (18,(42)(43)(44) or contained weak organic acids such as acetate, butyrate, or succinate (19,(45)(46)(47). This suggests that the plasma membrane of yeast is permeable not only to NH 4 ϩ but also to other weak acids.…”

Section: Nh 4 ϩ -Mediated Acidification Of the Yeast Vacuolementioning

confidence: 99%

Alternative Mechanisms of Vacuolar Acidification in H+-ATPase-deficient Yeast

Plant¹,

Manolson²,

Grinstein³

et al. 1999

Journal of Biological Chemistry

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Acidification of the endosomal/lysosomal pathway by the vacuolar-type proton translocating ATPase (VATPase) is necessary for a variety of essential eukaryotic cellular functions. Nevertheless, yeasts lacking VATPase activity (⌬vma) are viable when grown at low pH, suggesting alternative methods of organellar acidification. This was confirmed by directly measuring the vacuolar pH by ratio fluorescence imaging. When ⌬vma yeasts were cultured and tested in the acidic conditions required for growth of V-ATPase-deficient mutants, the vacuolar pH was 5.9. Fluid-phase pinocytosis of acidic extracellular medium cannot account for these observations, because the V-ATPase-independent vacuolar acidification was unaffected in mutants deficient in endocytosis. Similarly, internalization of the plasmalemmal H ؉ -ATPase (Pma1p) was ruled out, because overexpression of Pma1p failed to complement the ⌬vma phenotype and did not potentiate the vacuolar acidification. To test whether weak electrolytes present in the culture medium could ferry acid equivalents to the vacuole, wildtype and the ⌬vma yeasts were subjected to sudden changes in extracellular pH. In both cell types, the vacuoles rapidly alkalinized when external pH was raised from 5.5 (the approximate pH of the culture medium) to 7.5 and re-acidified when the yeasts were returned to a medium of pH 5.5. Importantly, these rapid pH changes were only observed when NH 4 ؉ , routinely added as a nitrogen source, was present. The NH 4 ؉ -dependent acidification was not due to efflux of NH 3 from the vacuole, as cells equilibrated to pH 7.5 in the absence of weak electrolytes rapidly acidified when challenged with an acidic medium containing NH 4 ؉ . These findings suggest that although NH 3 can act as a cell-permeant proton scavenger, NH 4 ؉ may function as a protonophore, facilitating equilibration of the pH across the plasma and vacuolar membranes of yeast. The high concentration of NH 4 ؉ frequently added as a nitrogen source to yeast culture media together with effective NH 4 ؉ transporters thereby facilitate vacuolar acidification when cells are suspended in acidic solutions.Acidification of defined endomembrane compartments along the endocytic and secretory pathways is essential for cellular function. Intraorganellar acidification appears to control vesicular traffic (1) as well as receptor ligand dissociation within endosomes (1). Similarly, acidification is thought to be essential for protein degradation in lysosomes (2) and for microbial elimination in phagosomes (3). In yeast and plants acidification of the vacuole provides the driving force for secondary transport of a variety of ions and metabolites (4 -7).Acid equivalents are concentrated in the lumen of these organelles by active H ϩ pumping mediated by the vacuolartype ATPase (V-ATPase), 1 an evolutionarily conserved multimeric enzyme (see Refs. 8 -11 for review). Considering the array of critical cellular functions that depend on the acidification generated by the V-ATPase, this enzyme would be predicted to be e...

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Distribution of individual cytoplasmic pH values in a population of the yeastSaccharomyces cerevisiae

Cited by 33 publications

References 15 publications

A glutamate residue in the catalytic center of the yeast chorismate mutase restricts enzyme activity to acidic conditions

A glutamate residue in the catalytic center of the yeast chorismate mutase restricts enzyme activity to acidic conditions

Mechanism of Genetic Complementation of Ammonium Transport in Yeast by Human Erythrocyte Rh-associated Glycoprotein

Alternative Mechanisms of Vacuolar Acidification in H+-ATPase-deficient Yeast

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