Proton Motive Force and Phosphorylation Potential in Thylakoids

1985 ◽  
Vol 12 (1) ◽  
pp. 21 ◽  
Author(s):  
AB Hope ◽  
G Doherty ◽  
P Stainer
Keyword(s):  
Steady State ◽  
Proton Motive Force ◽  
Light Period ◽  
Proton Flux ◽  
Motive Force ◽  
Potential Difference ◽  
Type B ◽  
Phosphorylation Potential ◽  
The Relationship ◽  
Degree Of Coupling

The relationship between phosphorylation potential and the transthylakoid pH difference (ΔpH) was explored in class C pea chloroplasts under two conditions: (a) in the light, in a steady state following photophosphorylation, where ΔpH was varied with addition of nigericin, and (b) in the dark after a light period in the presence of dithioerythritol to promote ΔTP-hydrolase activity. In experiments of type (b), the phosphorylation potential was varied through the concentrations of adenylates. In both conditions there was a correlation between the phosphorylation potential and ΔpH. The slope of the relationship between the two in the light was taken as giving the product n.q of the mechanistic stoichiometry, n with q, the degree of coupling of the ATP-synthetase reaction with the proton flux. This product was 1.9 � 0.1, implying n=2 if q=0.95, or n=3 if q=0.66. The data from both types of experiment required a transthylakoid potential difference of up to + 155 mV for the phosphorylation potential to be poised against the proton motive force as in a macrochemiosmotic theory.

scholarly journals The effects of partial and selective reduction in the components of the proton-motive force on lactose uptake in Escherichia coli

1981 ◽  
Vol 200 (3) ◽  
pp. 583-589 ◽  
Author(s):  
S Ahmed ◽  
I R Booth
Keyword(s):  
Escherichia Coli ◽  
Steady State ◽  
Membrane Potential ◽  
Selective Reduction ◽  
Proton Motive Force ◽  
Motive Force ◽  
Ph Gradient ◽  
A Value ◽  
The Relationship ◽  
Lactose Transport

The relationship between the steady state lactose accumulation (delta plac) and the magnitude of the membrane potential (delta psi) and pH gradient (delta pH) has been studied at pHo5.5 and pHo7.5. An attempt has been made to differentiate between two possible means by which lactose accumulation may be reduced below the proton-motive force (delta p). Firstly, that delta psi and delta pH are not equivalent in driving lactose transport and secondly, that ‘slip’ reactions (beta-galactoside exit via the carrier without a proton) may reduce accumulation. The data support the latter; however, our conclusions are tempered by the observation that the apparent stoichiometry (delta plac/delta p) increases to a value of at least 2 at values of delta p below 130 mV.

Photophosphorylation in Chloroplasts With Varied Proton Motive Force (PMF): I. The PMF and Its Onset

1982 ◽  
Vol 9 (4) ◽  
pp. 385 ◽  
Author(s):  
AB Hope ◽  
D Ranson ◽  
PG Dixon
Keyword(s):  
Steady State ◽  
Proton Translocation ◽  
State Level ◽  
Proton Motive Force ◽  
Motive Force ◽  
Diffuse Double Layer ◽  
Layer Potentials ◽  
Electrochromic Shift ◽  
Single Turnover ◽  
Actinic Light

The transthylakoid pH difference (ΔpH) following shuttered periods of actinic light from 10 ms to 30 s duration was estimated from fluorescence quenching of N-(1-naphthyl)ethylenediamine or 9-aminoacridine in phosphorylating conditions, � valinomycin and � nigericin. ΔpH in controls varied from about 2 units after 10 ms to a maximum of 3.6 - 3.8 units in the steady state. The transthylakoid potential difference (ΔV), defined as the average electric potential energy for protons moving from the intrathylakoid spaces to the outside, was estimated from the size of ΔA520-500 (the electrochromic shift) during similar light periods, with a correction for diffuse-double-layer potentials on the outside and inside of the thylakoids. A relation between ΔA520-500 and ΔV followed from the assumption that the former signal during a single-turnover flash represented 30 mV between the insides of the thylakoid surfaces. On this basis ΔV rose rapidly to about 80 mV at ~25 ms, and declined thereafter, to reach a steady-state level of ~13 mV at 10-30 s. The total proton motive force (PMF) thus estimated rose to about 225 mV within 20 ms and remained constant (controls) or declined slowly (+nigericin). With added valinomycin + K+, the PMF rose from 120 mV at 10 ms to c. 190 mV in the steady state, corresponding to low values of ΔV throughout. The findings are discussed in relation to present concepts of electron transport, proton translocation and charge accumulation in chloroplast thylakoids, especially on the millisecond timescale, and compared with other estimates of ΔpH and ΔV.

scholarly journals Quantitative measurements of the proton-motive force and its relation to steady state lactose accumulation in Escherichia coli

1981 ◽  
Vol 200 (3) ◽  
pp. 573-581 ◽  
Author(s):  
S Ahmed ◽  
I R Booth
Keyword(s):  
Escherichia Coli ◽  
Steady State ◽  
Membrane Potential ◽  
Proton Motive Force ◽  
Motive Force ◽  
Ph Gradient ◽  
Experimental Conditions ◽  
Ph Values ◽  
Quantitative Measurements ◽  
Essential Prerequisite

The magnitude of delta psi (membrane potential), delta pH (pH gradient), lactose accumulation and cytoplasmic volume have been determined over a range of experimental conditions. A study of two probes of delta pH, benzoate and dimethyloxazolidene-2,4-dione (DMO), and four probes of delta psi, Rb+, K+, tetraphenylphosphonium (TPP+) and 3,3′-dipropylthiodicarbocyanine iodide, has been carried out. Benzoate and DMO are shown to be equivalent at pH values above the pK of DMO, but the latter may be less accurate below this pH. The cations TPP+ and Rb+ were found, by a number of criteria, to be equivalent, and TPP+ may be used in cells not pretreated with EDTA. These studies are an essential prerequisite to the use of TPP+ as a quantitative probe in untreated cells.

Energy charge, phosphorylation potential and proton motive force in chloroplasts

1980 ◽  
Vol 590 (1) ◽  
pp. 59-73 ◽  
Author(s):  
Christoph Giersch ◽  
Ulrich Heber ◽  
Yoshichika Kobayashi ◽  
Yorinao Inoue ◽  
Kazuo Shibata ◽  
...  
Keyword(s):  
Energy Charge ◽  
Proton Motive Force ◽  
Motive Force ◽  
Phosphorylation Potential
Sign in / Sign up

Export Citation Format

Share Document