scholarly journals Experimental discrimination between proton leak and redox slip during mitochondrial electron transport

1994 ◽  
Vol 297 (1) ◽  
pp. 27-29 ◽  
Author(s):  
M D Brand ◽  
L F Chien ◽  
P Diolez
Keyword(s):  
Oxygen Consumption ◽  
Proton Leak ◽  
Protonmotive Force ◽  
Proton Pumps ◽  
Proton Conductance ◽  
Turnover Rates ◽  
High Turnover ◽  
Mitochondrial Inner Membrane ◽  
Rate Of Oxygen Consumption ◽  
The Relationship

By measuring the relationship between protonmotive force and the increment in oxygen consumption by mitochondria treated with submaximal amounts of uncoupler, we have experimentally tested four different models of imperfect coupling of oxidative phosphorylation. The results show that the increased rate of oxygen consumption at high protonmotive force is explained entirely by the dependence on protonmotive force of the passive proton leak conductance of the mitochondrial inner membrane. There is no measurable contribution from redox-slip reactions in the proton pumps caused by high protonmotive force. Neither is there any contribution from increased proton conductance of the membrane or increased redox slip in the respiratory chain caused by high turnover rates of the complexes.

scholarly journals Effect of protonmotive force on the relative proton stoichiometries of the mitochondrial proton pumps

1991 ◽  
Vol 275 (1) ◽  
pp. 75-80 ◽  
Author(s):  
R P Hafner ◽  
M D Brand
Keyword(s):  
Oxygen Consumption ◽  
Oxygen Atom ◽  
Respiration Rate ◽  
Proton Leak ◽  
Protonmotive Force ◽  
Proton Pumps ◽  
Isolated Mitochondria

The rate of phosphorylation of ADP by isolated mitochondria respiring on succinate was set by addition of ATP, ADP or ADP plus malonate. We measured the rates of phosphorylation and respiration and the protonmotive force under each of these conditions. We measured the oxygen consumption required to drive the proton leak at the protonmotive force reached under each condition and subtracted it from the respiration rate during phosphorylation to determine the oxygen consumption driving phosphorylation. By dividing the rate of phosphorylation by the rate of respiration driving phosphorylation we calculated the mechanistic P/O ratio (number of molecules of ADP phosphorylated per oxygen atom reduced). This ratio was the same at high, intermediate and low values of protonmotive force, indicating that the relative stoichiometries of the mitochondrial protonmotive-force-producing and protonmotive-force-consuming pumps (i.e. H+/O:H+/ATP) are independent of the protonmotive force. This greatly weakens the case for a decrease in stoichiometry, or ‘slip’, in the mitochondrial proton pumps at high protonmotive force.

scholarly journals Mitochondrial proton conductance and H+/0 ratio are independent of electron transport rate in isolated hepatocytes

1995 ◽  
Vol 310 (2) ◽  
pp. 379-382 ◽  
Author(s):  
R K Porter ◽  
M D Brand
Keyword(s):  
Oxygen Consumption ◽  
Electron Transport ◽  
Electron Transport Rate ◽  
Isolated Hepatocytes ◽  
Transport Rate ◽  
Proton Pumps ◽  
Proton Conductance ◽  
Inner Membrane ◽  
Mitochondrial Inner Membrane ◽  
Electron Transport Complexes

In this paper we examine the non-linearity of the relationship between the proton electrochemical gradient across the mitochondrial inner membrane (delta p) and oxygen consumption of non-phosphorylating mitochondria in situ in hepatocytes. Models proposing to explain the non-linear relationship were tested experimentally. It was shown that the mitochondrial proton conductance and the number of protons pumped to the cytosolic side of the mitochondrial inner membrane by the electron transport complexes per oxygen atom consumed (H+/O ratio) are independent of electron transport rate in mitochondria in isolated hepatocytes. The non-linearity of the plot of delta p against the non-phosphorylating oxygen consumption is due to either a potential-dependent slippage of the proton pumps of the mitochondrial inner membrane and/or a potential-dependent leakage of protons back across the mitochondrial inner membrane.

The Non-Ohmic Proton Leak—25 Years On

1997 ◽  
Vol 17 (3) ◽  
pp. 251-257 ◽  
Author(s):  
David G. Nicholls
Keyword(s):  
Ion Transport ◽  
Respiratory Chain ◽  
Atp Synthesis ◽  
Proton Leak ◽  
Protonmotive Force ◽  
Proton Conductance ◽  
Inner Membrane ◽  
Ohm’S Law ◽  
Mitochondrial Inner Membrane ◽  
Proton Current

The proton conductance of the mitochondrial inner membrane can be quantified by applying Ohm's law to the experimentally determined protonmotive force and the proton current flowing around the proton circuit in the absence of ATP synthesis or ion transport. This last parameter is derived from the rate of State 4 respiration multiplied by the H+/O stoichiometry for the substrate. When the activity of the dehydrogenase supplying electrons to the respiratory chain is progressively increased the proton conductance increases rapidly when the protonmotive force is greater than 220 mV. The consequences of this non-ohmic relationship are discussed.

The relationship between cirral activity and oxygen uptake in Balanus balanoides

1965 ◽  
Vol 45 (2) ◽  
pp. 387-403 ◽  
Author(s):  
R. C. Newell ◽  
H. R. Northcroft
Keyword(s):  
Body Weight ◽  
Oxygen Consumption ◽  
Oxygen Uptake ◽  
Mantle Cavity ◽  
The Body ◽  
Effect Of Temperature ◽  
Zero Rate ◽  
Rate Of Oxygen Consumption ◽  
The Relationship ◽  
Balanus Balanoides

The rate of cirral beat of Balanus balanoides is related to the logarithm of the body weight as an exponential function. In any one animal, there is little effect of temperature on cirral activity between 7·5° and 10° C. Between 10° and 20° C, however, there is a rapid increase in cirral beat with temperature followed by a fall at temperatures above 20° C.Balanus balanoides exhibits a fast, medium and zero rate of oxygen consumption. These rates of oxygen consumption correspond with (a) normal cirral beating, (b) ‘testing’ activity with no cirral movement, and (c) with the closure of the mantle cavity. Both of the possible levels of oxygen uptake are related to the logarithm of the body weight in a logarithmic fashion over the temperature range 7·5°–22·5° C. Temperature affects the two rates of oxygen consumption differently. In the slower rate (rate B) there is an increase in the rate of oxygen consumption between 7·5° and 14° C but there is no significant increase in the rate of oxygen consumption between 14° and 22·5 C°.

scholarly journals On the role of the membrane proton conductance in the relationship between rate of respiration and protonmotive force

1985 ◽  
Vol 229 (3) ◽  
pp. 833-837 ◽  
Author(s):  
A Ghazi
Keyword(s):  
Experimental Data ◽  
Unique Function ◽  
Protonmotive Force ◽  
Proton Conductance ◽  
Chemiosmotic Theory ◽  
The Relationship ◽  
Recent Interpretation

The rate of respiration in mitochondria is not a unique function of the protonmotive force, depending on whether the protonmotive force is varied by addition of ADP or uncouplers. This result has been generally considered to contradict the chemiosmotic theory. Recently, O'Shea & Chappell [Biochem. J. (1984) 219, 401-404] claimed that this observation can be reconciled with the chemiosmotic theory, provided only that the proton conductance of the membrane is different in the presence of ADP or uncouplers. This hypothesis is shown here to be necessary but not sufficient to account for the experimental data and the reason for the contradiction between this recent interpretation and earlier interpretations is pointed out.

Heart rate as an indicator of oxygen consumption: influence of body condition in the king penguin

2001 ◽  
Vol 204 (12) ◽  
pp. 2133-2144 ◽  
Author(s):  
G. Froget ◽  
P. J. Butler ◽  
Y. Handrich ◽  
A. J. Woakes
Keyword(s):  
Heart Rate ◽  
Oxygen Consumption ◽  
Body Condition ◽  
Active Oxygen ◽  
The Body ◽  
Regression Equations ◽  
Oxygen Pulse ◽  
Rate Of Oxygen Consumption ◽  
The Impact ◽  
The Relationship

SUMMARY The use of heart rate to estimate field metabolic rate has become a more widely used technique. However, this method also has some limitations, among which is the possible impact that several variables such as sex, body condition (i.e. body fat stores) and/or inactivity might have on the relationship between heart rate and rate of oxygen consumption. In the present study, we investigate the extent to which body condition can affect the use of heart rate as an indicator of the rate of oxygen consumption. Twenty-two breeding king penguins (Aptenodytes patagonicus) were exercised on a variable-speed treadmill. These birds were allocated to four groups according to their sex and whether or not they had been fasting. Linear regression equations were used to describe the relationship between heart rate and the rate of oxygen consumption for each group. There were significant differences between the regression equations for the four groups. Good relationships were obtained between resting and active oxygen pulses and an index of the body condition of the birds. Validation experiments on six courting king penguins showed that the use of a combination of resting oxygen pulse and active oxygen pulse gave the best estimate of the rate of oxygen consumption V̇O2. The mean percentage error between predicted and measured V̇O2 was only +0.81% for the six birds. We conclude that heart rate can be used to estimate rate of oxygen consumption in free-ranging king penguins even over a small time scale (30min). However, (i) the type of activity of the bird must be known and (ii) the body condition of the bird must be accurately determined. More investigations on the impact of fasting and/or inactivity on this relationship are required to refine these estimates further.

The Respiratory Physiology of the Marine Nematodes Enoplus Brevis (Bastian) and E. Communis (Bastian)

1973 ◽  
Vol 59 (1) ◽  
pp. 255-266
Author(s):  
H. J. ATKINSON
Keyword(s):  
Oxygen Consumption ◽  
Body Size ◽  
Oxygen Tension ◽  
Dry Weight ◽  
Respiratory Physiology ◽  
Rate Of Oxygen Consumption ◽  
Oxygen Tensions ◽  
The Difference ◽  
Relationship Of ◽  
The Relationship

1. The rate of oxygen consumption of individual males of Enoplus brevis and E. communis was measured at 15 °C and at each of four oxygen tensions, 135, 75, 35, and 12 Torr, after at least 12 h experience of these conditions. 2. It was clearly demonstrated that the level of oxygen consumption of both species was reduced by each lowering of the imposed oxygen tension. 3. In all cases the oxygen consumption of each species fell with increasing body size. On a unit dry-weight basis the oxygen consumption of E. brevis is greater than that of the larger E. communis, but after allowing for the difference of body size the two species have more or less similar oxygen uptakes at all oxygen tensions. 4. In E. brevis oxygen tension influenced the relationship of body size and metabolism, the slope relating oxygen consumption and body weight becomes steeper with decreasing oxygen tension. This effect was not shown by E. communis. 5. Some general factors influencing the availability of oxygen to nematodes are considered.

The heart rate/oxygen consumption relationship during cold exposure of the king penguin: a comparison with that during exercise

2002 ◽  
Vol 205 (16) ◽  
pp. 2511-2517 ◽  
Author(s):  
G. Froget ◽  
Y. Handrich ◽  
Y. Le Maho ◽  
J.-L. Rouanet ◽  
A. J. Woakes ◽  
...  
Keyword(s):  
Heart Rate ◽  
Oxygen Consumption ◽  
Critical Temperature ◽  
Body Condition ◽  
Heart Beat ◽  
Lower Critical Temperature ◽  
Rate Of Oxygen Consumption ◽  
Free Ranging ◽  
The Relationship ◽  
Environmental Temperatures

SUMMARY This study investigated whether exposure to low ambient temperature could be used as an alternative to exercise for calibrating heart rate (fH)against rate of oxygen consumption(V̇O2) for subsequent use of fH to estimate V̇O2 in free-ranging animals. Using the relationship between the oxygen pulse (OP, the amount of oxygen used per heart beat) and an index of body condition (or nutritional index, NI), a relationship between fH and V̇O2 was established for resting king penguins exposed to a variety of environmental temperatures. Although there was a small but significant increase in the OP above and below the lower critical temperature (-4.9°C), there was no difference in the relationship obtained between the OP and body condition (NI)obtained above or below the lower critical temperature. These results were then compared with those obtained in a previous study in which the relationship between fH and V̇O2 had been established for king penguins during steady-state exercise. The relationship between OP and NI in the present study was not significantly different from the relationship between resting OP and NI in the previous study. However, the relationship was different from that between active OP and NI. We conclude that, at least for king penguins, although thermoregulation does not affect the relationship between resting OP and NI, temperature cannot be used as an alternative to exercise for calibrating fH against V̇O2 for subsequent use of fH to estimate V̇O2 in free-ranging animals.

scholarly journals Energetics of Sodium Transport in Frog Skin

1972 ◽  
Vol 59 (1) ◽  
pp. 60-76 ◽  
Author(s):  
F. L. Vieira ◽  
S. R. Caplan ◽  
A. Essig
Keyword(s):  
Oxygen Consumption ◽  
Sodium Transport ◽  
Frog Skin ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Stoichiometric Ratio ◽  
Straight Line ◽  
Rate Of Oxygen Consumption ◽  
Solution Bathing ◽  
The Relationship

Sodium transport and oxygen consumption were studied simultaneously in the short-circuited frog skin. Sodium transport was evaluated from Io/F, where Io is the short-circuit current measured with standard Ringer's solution bathing each surface and F is the Faraday constant. Oxygen tension was measured polarographically. Under a variety of circumstances the rate of oxygen consumption from the outer solution exceeded that from the inner solution, the ratio being constant (0.57 ± 0.09 SD). Both Io and the associated rate of oxygen consumption Jro declined nonlinearly with time, but the relationship between them was linear, suggesting that the basal oxygen consumption was constant. For each skin numerous experimental points were fitted by the best straight line. The intercept (Jro)Io=0 then gave the basal oxygen consumption, and the slope dNa/dO2 gave an apparent stoichiometric ratio for a given skin. The basal oxygen consumption was about one-half the total oxygen consumption in a representative untreated short-circuited skin. Values of dNa/dO2 in 10 skins varied significantly, ranging from 7.1 to 30.9 (as compared with Zerahn's and Leaf and Renshaw's values of about 18). KCN abolished both Io and Jro. 2,4-dinitrophenol (DNP) depressed Io while increasing Jro four- to fivefold. Anti-diuretic hormone stimulated and ouabain depressed both Io and Jro; in both cases apparent stoichiometric ratios were preserved.

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