Cytoplasmic pH, regulation

Roberts, J.K.M., Callis, J., Wemmer, D., Walbot, V. Jardetzky, O. (1984). Mechanisms of cytoplasmic pH regulation in hypoxic maize root tips and its role in survival under hypoxia. Proceedings of the National Academy of Sciences, USA, 81, 3379-83. 

J. H. Xia and J. K. M. Roberts, Improved cytoplasmic pH regulation, increased lactate efflux, and reduced cytoplasmic lactate levels are biochemical traits expressed in root tips of whole maize seedlings acclimated to a low-oxygen environment. P/anr P/iy.vto/. 105 651 (1994). 

Swallow, C. J., Grienstein, S., Sudbury, R. A., and Rotstein, O. D. (1991). Nitric oxide derived from L-arginine impairs cytoplasmic pH regulation by vacuolar type H ATP-ase in peritoneal macrophages./. Exp. Med. 174, 1009-1021. 

Note that, due to their different environment, the cytoplasmic and vacuole phosphates are completely separate, hence we have a means of access to cellular compartmentalisation. G6P is only present in the cytoplasm and can thus provide a confirmation of the pH measurement from the inorganic phosphate, when in sufficient concentration. A study of cytoplasmic pH regulation (in Fig. 7) shows that this pH can be selectively monitored during external pH evolutions. 

Lallemand, "Cytoplasmic pH Regulation in Acer pseudoplatanus Cells". 

ME Dowty, P Braquet. (1991). Effect of extracellular pH on cytoplasmic pH and mechanism of pH regulation in cultured bovine corneal endothelium Possible importance in drug transport studies. Int J Pharm 68 231-238. 

CJ Swallow, S Grinstein, OD Rotstein. (1990). A vacuolar type H+-ATPase regulates cytoplasmic pH in murine macrophages. J Biol Chem 265 7645-7654. 

An important factor in food safety is that bacteria can only survive in acidic environments by regulating their cytoplasmic pH (pH ). This is primarily driven by controlled movement of cations across the cell membrane. However, this ability to maintain the pH close to neutrality can be... 

One of the key features of ABA enhancement of Ik,oui is that it persists even when cytosolic Ca" concentrations are buffered to low levels by the inclusion of EGTA in the patch pipette solution during whole cell reeording. This suggests that elevated [Ca ],., is not involved in the activation of Ik.oui t>y ABA. Indeed, when [Ca ], is experimentally elevated from approximately 2 nM to 200 nM in whole-cell patch clamp experiments, current through outward K channels is reduced [72], an effect which would oppose stomatal closure. At higher [Ca ],.y,s, outward current shows little Ca -sensitivity [23]. More recently, it has been shown that Ik oui sensitive to cytoplasmic pH. Its regulation by pH has consequences for ABA-induced closure, and will be discussed in Section... 

The cytoplasmic pH of f), acudoptuJla is scarcely influenced if cells are suspended for 1-3 h in media of different pH (fig.l). This demonstrates an efficient pH regulation. Illumination of cells causes a slight alkalization (0.1-0.3 pH units), whereas under anaerobiosis cytoplasmic pH drops by about 0.4-0.6 pH units (not shown). The dependence of photosynthesis of acMLophUla on external CO2 is complex (fig.2). At lower concentrations Michaelis-Menten kinetics are observed... 

Booth IR. (1985). Regulation of cytoplasmic pH in bacteria. Micmbiological Reviews, 49, 359-378. 

Plasma membranes of all cells investigated so far contain an electron transport system transferring electrons from NADH to an extracellular electron acceptor (for review, see Navas et al., 1994 and Chapter 4 of this volume). Electron transport across the plasma membrane is accompanied by release of protons from the cell, presumably due to an activation of the Na+/H+ antiport (Sun et a/., 1988). Since proton release and the concomitant increase in cytoplasmic pH have been connected to growth stimulation (Moolenar et al., 1983), it was proposed that the transplasma membrane redox system via proton release might also be involved in the regulation of proliferation. 

Figure 1. The general mechanism for ATP synthesis by aerobes and microaerobhiles. The environmental pH that is tolerated is pH 4 to 7. This pH is the same as that found in the periplasmic space unless there are specialized mechanisms for pH regulation such as urease. Over the range of pH from 4 to 7, various substrates are oxided via a series of electron acceptors which in turn are reoxidized by oriented redox complexes so that protons are exported electrogenically across the cytoplasmic membrane. This generates an interior negative potential and an inward pH gradient to provide the proton motive force for aerobic ATP S3mthesis and H gradient linked uptake or export of ions or solutes.

We now wish to focus our attention on the parameter (J /P)h+. From Tables 2 and 3, it is apparent that its value remains smaller than that of the parameter of all other ions. Some salient features of (J /P)h+ can be derived from some of our earlier calculations 23, They show that at fixed external conditions and internal pH, there are no marked effects of the internal variables and of Em on (Ja/p)h+, although the other parameters (Ja/p)i required to find back the internal conditions are changing. Conversely, at fixed internal conditions and external pH, the value of (Ja/P)h+ is also only weakly affected by changes of the external conditions. Finally, if all external and internal conditions are kept constant (Ja/p)h+ varies appreciably with the external pH in acid solutions (pH < 7). It is reasonable to conclude from all these facts that the role of the proton transfer in the course of the ionic transfer process between the external and internal phases is restricted to the cytoplasmic and vacuolar pH regulation. The proton transfer exerts a minor effect on the other internal parameters. 

During the last ten years, it has become apparent that calcium-dependent papain-like peptidases called calpains (EC 3.4.22.17) represent an important intracellular nonlysosomal enzyme system [35][36], These enzymes show limited proteolytic activity at neutral pH and are present in virtually every eukaryotic cell type. They have been found to function in specific proteolytic events that alter intracellular metabolism and structure, rather than in general turnover of intracellular proteins. Calpains are composed of two nonidentical subunits, each of which contains functional calcium-binding sites. Two types of calpains, i.e., /i-calpain and m-calpain (formerly calpain I and calpain II, respectively), have been identified that differ in their Ca2+ requirement for activation. The activity of calpains is regulated by intracellular Ca2+ levels. At elevated cytoplasmic calcium concentrations, the precursor procal-pain associates with the inner surface of the cell membrane. This interaction seems to trigger autoproteolysis of procalpain, and active calpain is released into the cytoplasm [37]. 

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