Na+ and K+ transport in a photodenitrifier, Rhodopseudomonas sphaeroides f.sp. denitrificans

1986 ◽  
Vol 64 (9) ◽  
pp. 946-952
Author(s):  
Balaram Kundu ◽  
D. J. D. Nicholas
Keyword(s):  
Proton Motive Force ◽  
Motive Force ◽  
Rhodopseudomonas Sphaeroides ◽  
Concomitant Increase ◽  
K Transport

Washed cells of Rhodopseudomonas sphaeroides f.sp. denitrificans depleted of cellular K+ by treatment with diethanolamine contained less than 5 mM K+. The K+-depleted cells accumulated 22Na+ only when there was no diethanolamine in the external buffer (50 mM Tris–HCl, pH 7.5). Studies with 22Na+-loaded cells indicate that this photodenitrifier had antiporters for Na+–H+, K+–Na+, and K+–H+ and lacked a respiration (denitrification) dependent Na+ pump. The K+–Na+ antiporter was electrogenic and required proton-motive force for its operation. Thus the addition of either NaCl or KCl to K+-depleted cells resulted in a depolarization of Δψ, both in light and in the dark, by 10–35 mV, which was partially compensated for by a concomitant increase (5–13 mV) in ΔpH.

scholarly journals K+/H+ antiport in the tobacco hornworm midgut: the K(+)-transporting component of the K+ pump.

1994 ◽  
Vol 196 (1) ◽  
pp. 361-373 ◽  
Author(s):  
A Lepier ◽  
M Azuma ◽  
W R Harvey ◽  
H Wieczorek
Keyword(s):  
Plasma Membrane ◽  
Plasma Membranes ◽  
Tobacco Hornworm ◽  
Proton Motive Force ◽  
Motive Force ◽  
Apical Plasma Membrane ◽  
Lectin Staining ◽  
Sds Page ◽  
K Transport ◽  
Midgut Lumen

The midgut of the tobacco hornworm secretes K+ across the apical plasma membrane of its goblet cells. This secondary K+ transport results from K+/H+ antiport energized by the proton-motive force generated by a primary, H(+)-transporting plasma membrane V-ATPase. Thus, the lepidopteran midgut constitutes a well-established example of the emerging concept that the proton-motive force is an alternative to the classical sodium-motive force for the energization of animal plasma membranes. K+/H+ antiport in the tobacco hornworm midgut is electrophoretic, exchanging 2H+ for 1K+. Under physiological conditions, it is energized by the voltage component of the proton-motive force. The strong coupling of electrophoretic K+/2H+ antiport with the electrogenic V-ATPase provides, in principle, the minimal device for the alkalization of the midgut lumen to pH values higher than 11. K+/H+ antiport is insensitive to bafilomycin A1, but is inhibited by amiloride or Concanavalin A. Lectin staining of blots after SDS-PAGE revealed several glycosylated polypeptides in the goblet cell apical membrane which are not part of the V-ATPase and thus are candidates for the antiporter protein. Current efforts are focused on the isolation of the K+/H+ antiporter.

Proton motive force in a photodenitrifier, Rhodopseudomonas sphaeroides forma specialis denitrificans

1986 ◽  
Vol 64 (4) ◽  
pp. 328-336
Author(s):  
Balaram Kundu ◽  
D. J. D. Nicholas
Keyword(s):  
Electron Transport ◽  
Dark Respiration ◽  
Photosynthetic Electron Transport ◽  
Proton Motive Force ◽  
Motive Force ◽  
Antimycin A ◽  
Rhodopseudomonas Sphaeroides ◽  
Ph Values ◽  
Carbonyl Cyanide ◽  
Light Inhibition

The washed cells of Rhodopseudomonas sphaeroides f.sp. denitrificans developed a Δp of about −175 to −200 mV during denitrification in the dark and −200 to −245 mV in the light. With NO2− as the terminal acceptor, Δp was less than with NO3−, N2O, or O2. The values of Δψ in the dark were about −150 mV for NO3− and N2O and −140 mV for NO2−. During photodenitrification with NO3−, NO2−, or N2O or respiration to O2 in light, Δψ ranged between −152 and −167 mV. Like Δψ, the ΔpH was higher in light than in the dark, resulting in a 20- to 30-mV increase in Δp during illumination with NO3−, NO2−, or N2O as the acceptor. Both ΔpH and Δψ were reduced at higher pH values (≥ 7.5). Changes in pH in response to O2 in the light were less than those in the dark, indicating light inhibition of O2 respiration. The cells maintained a reasonably high Δp without addition of a substrate or when inhibitors were used; the cells retained a fairly high Δψ even in the presence of an inhibitor. However, ΔpH was appreciably lowered and in some cases it was almost abolished when either KCN, rotenone, NaN3, carbonyl cyanide m-chlorophenylhydrazone (CCCP), 2,4-dinitrophenol, N,N′-dicyclohexylcarbodiimide, antimycin A, or 2-n-heptyl-4-hydroxyquinoline-N-oxide (HOQNO) was used. The combination of an uncoupler (e.g., CCCP) and an electron transport effector (e.g., antimycin A) further reduced the ΔpH. Antimycin A and HOQNO were more effective in inhibiting photosynthetic electron transport to NO3−, NO2−, N2O, or O2 than the dark respiration to these substrates. Dibromomethylisopropyl-p-benzoquinone, a quinone antagonist, markedly reduced ΔpH in light with NO3−, NO2−, N2O, or O2 as the terminal acceptor, indicating that photosynthetically generated electrons are used for denitrification in this bacterium.

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