Transmembrane Proton Electrochemical Gradients in Dark Aerobic and Anaerobic Cells of the Cyanobacterium (Blue-Green Alga) Anacystis nidulans

Abstract

The transmembrane proton electrochemical potential gradient A;&H+ in whole cells of Anacystis nidulans was measured in aerobic and anaerobic dark conditions using the distribution, between external medium and cell interior, of radioactively labeled weak acids (acetylsalicyclic acid, 5,5-dimethyloxazolidine-2,4-dione) or bases (imidazole, methylamine), and permeant ions (tetraphenylphosphonium cation, thiocyanate anion), as determined by flow dialysis. Alternatively, the movements across the plasma membrane of ApH-indicating atebrin or 9-aminoacridine, and of A4-indicating 8-anilino-1-naphthalenesulfonate were qualitatively followed by fluorescence measurements. Attempts were made to discriminate between the individual chemiosmotic gradients across the cytoplasmic (plasmalemma) and the intracytoplasmic (thylakoid) membranes. By use of the ionophores nigericin, monensin, and valinomycin, the components of the proton motive force, namely the proton concentration gradient ApH and the electric membrane potential AA' were shown to be mutually exchangeable within the range of external pH values tested (3.2-11.0). Both components were depressed by the uncoupler carbonylcyanide mchlorophenylhydrazone, though inhibition of ApH was much more pronounced than that of A4', notably in the alkaline pH. range. The total proton electrochemical gradient across the plasma membrane was significantly higher in aerobic than in anaerobic cells and increased markedly (i.e. became more negative) towards lower pH. values. This increase was paralleled by a similar increase in the rate of endogenous respiration of the cells. At the same time the ATPase inhibitor dicyclohexylcarbodiimide only slightly affected the proton motive force across the plasma membrane of aerobic cells. The results will be discussed in terms of a respiratorily competent plasma membrane in Anacystis nidulans. plasma membranes of higher plant cells (4, 5). Fundamentally, the gradient incorporates two components, the proton concentration gradient (ApH) and the electric membrane potential (A+), AMH+ (mv) = AA -60 ApH (at 35C), which are bioenergetically equivalent and mutually exchangeable (3, 25).Chemiosmotic parameters have been studied in whole cells (8, 10, 30) and isolated thylakoid vesicles (24) of cyanobacteria, albeit with primary focus on photosynthetic energization of the membranes (see Peschek [27] for review). With respect to the chemiosmotic theory intact cyanobacteria are challenging experimental systems since these 'uncompartmentalized' prokaryotes nevertheless do contain two osmotically autonomous intracellular compartments, namely the cytoplasmic space (surrounded by the plasma membrane) and the intrathylakoid space (surrounded by the thylakoid membrane). Unfortunately, satisfactory biochemical separation and individual characterization of plasma and thylakoid membranes, respectively, has not yet been achieved with cyanobacteria. However, several independent lines of evidence have shown that, in A. nidulans, the plasma membrane contains a respir...

pH determines the energetic efficiency of the cyanobacterial CO 2 concentrating mechanism

“…S8). This is expected because the photosynthetic light reactions pump H + from the cytosol into the thylakoid lumen (44) and the pH values are consistent with previous measurements of cytosolic pH in cyanobacteria (45)(46)(47)(48). The pH in the light coincides well with our prediction of an optimal cytosolic pH range for carbon-fixing cyanobacteria.…”

Nature of the Light-Induced H+ Efflux and Na+ Uptake in Cyanobacteria

“…3). Raising the external pH from 6.0 to 8.0 leads to a considerable decrease of the AAH' (19,30) since the hyperpolarization of the PM, on alkalinization of the medium, is too small to compensate for the change in ApH between the cytoplasm and the medium. Thus, while the driving force for the different processes involved in net proton transport should have been affected by the pH, it is possible that the lack of a pH effect, on the stimulation of acidification by amiloride, was due to a kinetic effect.…”

“…The interpretation of the data in Figure 5 and Table III is complicated by the following considerations: (a) although the cells were exposed to 22Na+ for only 7 s, it is not clear whether unidirectional Na+ influx was observed; (b) the kinetic parameters as well as the driving force for H+ and Na+ transport might also be affected by the alteration ofthe electrochemical potential of Na+ and H+ upon illumination; and (c) the relative role played by the Na+/H+ antiporter and the other means for Na+ transport such as Na+ uniport might be affected by the hyperpolarization of the PM upon illumination; supply of Ci or the alteration of extracellular pH (19,30). A significant rate of Na+ influx via a uniport system might explain the large effect of light on Na4 uptake (Fig.…”

Tetraphenylphosphonium cation (TPP+) is not a reliable membrane potential probe in the cyanobacterium Synechococcus R‐2 PCC 7942

“…Many of the reported membrane potential determinations for blue-green algae are based solely on the use of lipophilic cation probes (Kaplan et al, 1980 ;Reed et al, 1980 ;Zdrou & Tromballa, 1981 ;Kaplan et al, 1982 ;Miller et al, 1984 ;Reinhold et al, 1984 ;Zenvirth et al, 1984 ;Kaplan, 1985 ;Peschek et al, 1985 ;Budd & Kerson, 1987 ;Kaplan et al, 1989Kaplan et al, , 1991. Some of the above studies did not take proper account of the extensive binding of lipophilic cations to the surfaces of cells and so their estimates of the membrane potential are inaccurate.…”

“…Quantitative estimates of membrane potential are needed for thermodynamic analyses of ion transport (Peschek et al, 1985(Peschek et al, , 1988). …”