Proton leakage

Giannini, J.L., Holt, J.S., Briskin, D.P. The effect of glyceollin on proton leakage in Phytophthora megasperma f.sp. glycinea plasma membrane and red beet tonoplast vesicles. Plant Sci 1990 68 39-45. 

To determine the basis for this regular variation in rate of proton leakage, several characteristics of the mitochondria were measured, including inner membrane surface area per unit of matrix volume and fatty acid composition of mitochondrial membrane phospholipids. The largest share (about 70%) of the variation in proton flux rate appears to be due to dififer-... 

Concentrations of the products Due to the proton leakage through associated AEMs, the maximum concentration of mineral acid products is 2-3 and 5 N for organic acids. Due to the hydroxide ion leakage through the associated CEM, the maximum concentration of the base produced is 4.5 N. 

Lorrain, Y., Pourcelly, G., and Gavach, C. Influence of cations on the proton leakage through anion-exchange membranes. J. Membr. 

Disregarding proton leakage and assuming that the glycerol phosphate shutde is in operadon, 38 ATP would be produced from the aerobic oxidation of a glucose molecule. If the malate shutde is in operadon, only 36 ATP would be produced. 

Consideration of relative proton affinities alone is not sufficient to explain the directionality of transport in proton pumps. For efficient proton pumping it is essential that the activated proton (state 2) cannot flow back to group A, which thermodynamically would be dictated by the fact that A has much higher proton affinity than C. To that effect, relative insulation to proton transport in state 2 is required either between B and A, or alternatively, between A and surface I. This requirement is often described in terms of an alternating access model [Jardetzky, 1966] and is now fairly well understood in bacteriorhodopsin [Lanyi, 1999]. Likewise, proton leakage from C to B must be prevented in step 4, where B has a much higher proton affinity than C. In the depicted scheme (Fig.2), the back flow of is hampered by the high proton activity of C relative to O, so that proton relay to B from A is rapid compared to alternative reprotonation from O via C. 

One may speculate that a cold-induced tightening of the thylakoid membrane may be important e.g. for reducing proton leakage (see Gilmore, 1997), and that the cold-hardening process lowers the temperature threshold for this event considerably. 

Y. Lorrain, G. Pourcelly and C. Gavach, Influence of the proton leakage through anion exchange membranes,/ Membr. Sci., 1996, 110, 181-190. 

It was found that even few damaged and degraded copies of Dl protein could lead to extensive proton leakage and cause very rapid loss of trans-thylakoid proton gradient. ... 

Other acids with preservative action include benzoic acid (CgH COOH), the use of which has increased in recent years in animal feed. In its chemically pure form, this acid is a white granular or crystalline powder, however the main form used is sodium benzoate, due to its higher solubility in water. Benzoate inhibits yeasts more than moulds or bacteria. The undissociated form of benzoic acid, as well as sodium benzoate, is essential to its antimicrobial activity, as both are soluble in cell walls and facilitate proton leakage across membranes. This elevates energy requirements to maintain the internal cell pH. 

We have seen in the previous pages how the formation of ATP from ADP by oxidative phosphorylation depends on both a flow of protons (a proton current) and a flow of electrons (an electron current). Inevitably there will be consequences if leakage of either protons or electrons occurs. Proton leakage is associated with thermogenesis. Electron leakage is associated with the formation of reactive oxygen species (ROS), which can be extremely toxic. 

Although more experimental work is needed, it does seem clear that there is diminished capacity in many obese people for thermogenesis induced by dietary fat. The defect seems to be associated with brown fat. It could be that the amount of tissue is inadequate, or that there is a difference in the proton-leakage pathway, or that there is a failure at some stage of the switching-on process. 

Whereas phosphorylation efficiency dropped during ADP limitation under normoxia, P 0 ratios were conservatively five-fold higher under severe hypoxia, when oxygen consumption was limited by oxygen supply. A reduction in proton leakage across the inner membrane under hypoxia could potentially explain the observation, which would decrease state 4 respiration. The proton permeability of the inner mitochondrial membrane is dependent on the physical properties of... 

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