Brønsted acids bounded to the mitochondrial membranes as a substrate for ATP synthase

Abstract

158Starting from 1961, two models for transforma tion of the energy of oxidation reactions in mito chondria have been discussed in the literature. The model of Mitchell [1] implies that the multienzyme phosphorylation system can work in a dissociated form, while the other model (by Williams) considers a supercomplex [2].We have earlier demonstrated that the phosphory lation system is able to function in both modes, corre sponding to two structural states of mitochondria [3]. The operation modes of the phosphorylating system are provided by the system of mitochondrial volume regulation [4,5].In hypotonic media under conditions of low amplitude mitochondrial swelling, the Williams model considers protons (unstably bound to the membrane supercomplex as Brønsted acids) as a substrate for ATP synthase.In 1976, we demonstrated the possibility to use a Brønsted acid as a substrate for ATP synthase using a model system. In these experiments, ATP synthase was sorbed at the octane-water interface. In this sys tem, ATP synthesis was observed in the presence of ADP and phosphate, and the gradient of a Brønsted acid (pentachlorophenol) at the octane-water inter face was used as a source of energy; the gradient was created by adding pentachlorophenol to the octane phase [6].On the bilayer membrane, we have found the cata lysts that selectively accelerate dissociation of Brøn sted acids [7]. This allowed us to find [8] that a non equilibrium fraction of Brønsted acids with excess free energy was formed on the surface of mitoplasts (mito chondria without the outer membrane), provided that H + pumps function.The goal of this work was to prove the formation of Brønsted acids during ATP synthesis on the mito chondrial membranes.A tightly joining of the cristae (Figs. 1 and 2) and, correspondingly, the joining of the outer and inner membranes should be expected. In this process, a two membrane structure of mitoplasts is formed of the outer and inner membranes. Since the outer mem brane is well permeable ("transparent") for hydrogen ions in course of proton pumping, this structure should function as an integral whole interacting with hydrogen ions, possessing excess free energy (accord ing to the scheme in Fig. 1b).We have earlier demonstrated that the measure ment of surface ζ potential (using a Zetasizer Nano ZS device) of mitoplasts can be efficiently used for detecting formation of nonequilibrium Brønsted acids in functional states [8].To selectively accelerate dissociation of mem brane bound Brønsted acids, possessing excess free energy, we increased the concentration of catalyst (HEPES) [7].The measurements were performed in the media with a tonicity of 350 and 120 mOsm. In this experi ment, we compared the measured ζ potential on the surface of functional mitochondria during ATP syn thesis under isotonic and hypotonic conditions. The experiments conducted under hypotonic conditions have demonstrated (Table 1) that the changes in ζ potential on the mitochondrial surface regularly cor relate with the changes in ζ potential on t...

Mechanism of long‐range proton translocation along biological membranes

“…Numerous studies of the past two decades [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] indicate that the local model is more likely to be realized in real cells. The experiments, while often not unambiguous [23][24][25][26], did reveal however a puzzling property of protons migrating along the membrane surface -they appear to remain on the surface for too long, making surface transport surprisingly long-distant, up to tens of micrometers.…”

On local coupling of electron transport and ATP-synthesis system in mitochondria. Theory and experiment

“…The same effect was observed on phosphorylating mitochondria (in the presence of substrates: succinate, ADP, phosphate) under conditions of close docking of the inner and outer mitochondrial membranes in medium with decreased tonicity (120 mOsm) [15].…”

“…In our works, we showed experimentally the appear ance of membrane bound Bronsted acids carrying free energy excess on membranes of mitoplasts [13] and mito chondria [14,15]. Based on these experiments, we wrote a full equation of the thermodynamic potential of hydro gen ions (ΔG) as the sum of the electrochemical Mitchell's potential (ΔμH) and the solvation potential (Δμ solv ) resulting due to partial dehydration of membrane bound protons:…”

Oligomeric hypercomplex of the complete oxidative phosphorylation system in heart mitochondria

“…Proton binding at the interface was firstly reported in the biological system during the functioning of rhodopsin proton pumps (34). It was also shown that the operation of proton pumps in intact mitochondria and mitochondria without outer membranes leads to the formation of the membrane-bound protons fraction (35,36). Therefore, the protons with an excess of free energy may be retained on the membrane-water interface and used for ATP synthesis.…”