http://tinyurl.com/5a93sf The discovery in 1861 by Louis Pasteur that more yeast is formed aerobically than anaerobically per gram of glucose was the first clue to the difference in efficiency of glycolysis and oxidative phosphorylation. During the first half of the 20th century the pathway of glycolysis was untraveled. Individual enzymes and cofactors were isolated and characterized. A reconstituted system of all enzymes and cofactors catalyzed steady-state glycolysis, provided an appropriate ATPase was added. The need for an ATPase, clearly demonstrated in 1945 by Otto Meyerhof, remains an important aspect of glycolysis that has been sorely neglected by textbooks. The coupling of oxidation and phosphorylation and the formation of the high- energy intermediate 1,3-diphosphoglycerate, discovered by Otto Warburg, are the key reactions of glycolysis. A high-energy intermediate formed during this process was identified as a thiolester. Early concepts of the mechanism of oxidative phosphorylation based on this model led to some frustrating and confusing years of search for high-energy intermediates. Important contributions from the laboratories of Boyer, Cohn, Chance, Green, Lardy, and Lehninger elucidated the properties of the mitochondrial process. Then Peter Mitchell proposed in 1961, 100 years after the publication by Pasteur, that the "high-energy intermediate" is an electrochemical proton gradient generated by the electron transport chain and utilized by a proton turbine (the mitochondrial ATPase complex) to generate ATP. This concept is now widely accepted. Several problems remain to be solved. How are the protons translocated during electron transport? How many protons per site? What is the mechanism of ATP generation during proton flux via the mitochondrial ATPase? -- http://tinyurl.com/5hm8f3 Mathematical model for carbohydrate energy metabolism. Mechanism of the Pasteur effect The simple mathematical model based on the stoichiometric structure of carbohydrate metabolism and the only allosteric regulation presented, i. e. activation of phosphofructokinase by AMP, was used to study the mechanism of the Pasteur effect, e. g. interrelationship of glycolysis, the Krebs cycle and H-transporting shuttles at varying rates of oxidative phosphorylation and ATPase load. It was shown that the mechanism of the Pasteur effect is based on the presence of two negative feed-back mechanisms in carbohydrate metabolism, namely by the level of ATP in glycolysis and by the level of mitochondrial NADH in the Krebs cycle and H-transporting shuttles. It was also shown that the value and sign of the Pasteur effect depend on the level of ATPase load. The role of this phenomenon in stabilization of ATP in the cell is discussed. The effects of changes in the allosteric properties of phosphofructokinase and low activity of H-transporting shuttles on the Pasteur effect was studied. It was shown that the low values of the pasteur effect in tumour tissues are mainly determined by an insufficient activity of oxidative phosphorylation. http://tinyurl.com/5drvwq Quantitative analysis of some mechanisms affecting the yield of oxidative phosphorylation The purpose of this work was to show how the quantitative definition of the different parameters involved in mitochondrial oxidative phosphorylation makes it possible to characterize the mechanisms by which the yield of ATP synthesis is affected. Three different factors have to be considered: (i) the size of the different forces involved (free energy of redox reactions and ATP synthesis, proton electrochemical difference); (ii) the physical properties of the inner mitochondrial membrane in terms of leaks (H+ and cations); and finally (iii) the properties of the different proton pumps involved in this system (kinetic properties, regulation, modification of intrinsic stoichiometry ). The data presented different situations where one or more of these parameters are affected, leading to a different yield of oxidative phosphorylation. (1) By manipulating the actual flux through each of the respiratory chain units at constant protonmotive force in yeast mitochondria, we show that the ATP/O ratio decreases when the flux increases. Moreover, the highest efficiency was obtained when the respiratory rate was low and almost entirely controlled by the electron supply. (2) By using almitrine in different kinds of mitochondria, we show that this drug leads to a decrease in ATP synthesis efficiency by increasing the H+/ATP stoichiometry of ATP synthase (Rigoulet M et al. Biochim Biophys Acta 1018: 91-97, 1990). Since this enzyme is reversible, it was possible to test the effect of this drug on the reverse reaction of the enzyme i.e. extrusion of protons catalyzed by ATP hydrolysis. Hence, we are able to prove that, in this case, the decrease in efficiency of oxidative phosphorylation is due to a change in the mechanistic stoichiometry of this proton pump. To our knowledge, this is the first example of a modification in oxidative phosphorylation yield by a change in mechanistic stoichiometry of one of the proton pumps involved. (3) In a model of polyunsaturated fatty acid deficiency in rat, it was found that non-ohmic proton leak was increased, while ohmic leak was unchanged. Moreover, an increase in redox slipping was also involved, leading to a complex picture. However, the respective role of these two mechanisms may be deduced from their intrinsic properties. For each steady state condition, the quantitative effect of these two mechanisms in the decrease of oxidative phosphorylation efficiency depends on the values of different fluxes or forces involved. (4) Finally the comparison of the thermokinetic data in view of the three dimensional-structure of some pumps (X-ray diffraction) also gives some information concerning the putative mechanism of coupling (i.e. redox loop or proton pump) and their kinetic control versus regulation of mitochondrial oxidative phosphorylation. http://tinyurl.com/65arnv The roots of bioenergetics Understanding metabolic energy transformation began with the realization of an 'intrusion' of phosphate into the mechanism of alcoholic fermentation. The discovery of an analogous participation of phosphate in muscle glycolysis connected the metabolic generation of energy-rich phosphate bonds fed into a common transmitter, adenosine triphosphate (ATP), with the production of mechanical energy through the finding that the phosphoryl group of creatine phosphate transferred to ATP could supply the energy for muscle contraction. In this way, a functional applicability of the energy of the phosphate bond was first shown. This observation was soon followed by the recognition that the phosphoanhydride bond of ATP provided the driving force in biosynthetic reactions; in this type of bond, metabolic energy apparently collects before it is transmitted for functional and biosynthetic use. The storage of energy in ATP was first detected in anaerobic energy-yielding reactions but soon was also found in respiratory and photosynthetic energy production. However, the mechanism by which energy derived from metabolites was converted into phosphate-bond energy in the latter processes appeared to differ from that of anaerobic energy transmission. Whereas phosphorylated compounds mediate the latter in homogeneous solutions, aerobic phosphorylation and photophosphorylation in prokaryotes seem to require special submembranous structures; and in eukaryotes, energy conversion is a function of special organelles, the mitochondria and chloroplasts. The evolutionary aspects of the transition from prokaryotes to eukaryotes are of considerable interest. In conclusion, the relevance of an apparent prokaryotic origin of the energy-transforming organelles in the eukaryotes will be commented on. --

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