Phosphorylation, adenosine aerobic

Figure 22.17 Summary of mechanisms to maintain the ATP/ADP concentration ratio in hypoxic myocardium. A decrease in the ATP/ADP concentration ratio increases the concentrations of AMP and phosphate, which stimulate conversion of glycogen/ glucose to lactic acid and hence ATP generation from glycolysis. The changes also increase the activity of AMP deaminase, which increases the formation and hence the concentration of adenosine. The latter has two major effects, (i) It relaxes smooth muscle in the arterioles, which results in vasodilation that provides more oxygen for aerobic ATP generation (oxidative phosphorylation). (ii) It results in decreased work by the heart (i.e. decrease in contractile activity), (mechanisms given in the text) which decreases ATP utilisation.

Cyanide is described as a cellular toxin because it inhibits aerobic metabolism. It reversibly binds with ferric (Fe " ") iron-containing cytochrome oxidase and inhibits the last step of mitochondrial oxidative phosphorylation. This inhibition halts carbohydrate metabolism from citric acid cycle, and intracellular concentrations of adenosine triphosphate are rapidly depleted. When absorbed in high enough doses, respiratory arrest quickly ensues, which is probably caused by respiratory muscle failure. Cardiac arrest and death inevitably follow. 

Mitochondria (singular = mitochondrion) are the so-called "power plants" of eukaryotic cells because they are the major source of energy for these cells under aerobic conditions (when oxygen is present). Mitochondria are the sites where complex processes involved in energy generation (such as electron transport and oxidative phosphorylation) are found. The product of mitochondrial action is chemical energy stored in the form of adenosine triphosphate, more commonly called ATP. 

Aerobic respiration. Process in which compounds are oxidized with oxygen serving as the terminal electron acceptor, nsnally accompanied by production of adenosine triphosphate (ATP) by oxidative phosphorylation. 

Substrate-level phosphorylation. Prodnction of adenosine triphosphate (ATP) by the direct transfer of a high-energy phosphate molecnle to adenosine diphosphate (ADP) dnring catabolism of a phosphorylated organic componnd. It occurs under both aerobic and anaerobic conditions. 

In eukaryotes, oxidative phosphorylation occurs in mitochondria, while photophosphorylation occurs in chloroplasts to produce ATP. Oxidative phosphorylation involves the reduction of O2 to H2O with electrons donated by NADH and FADH2 in all aerobic organisms. After, carbon fuels (nutrients) are oxidized in the citric acid cycle, electrons with electron-motive force is converted into a proton-motive force. Photophosphorylation involves the oxidation of H2O to O2, with NADP as electron acceptor. Therefore, the oxidation and the phosphorylation of ADP are coupled by a proton gradient across the membrane. In both organelles, mitochondria and chloroplast electron transport chains pump protons across a membrane from a low proton concentration region to one of high concentration. The protons flow back from intermembrane to the matrix in mitochondria, and from thylakoid to stroma in chloroplast through ATP synthase to drive the synthesis of adenosine triphosphate. Therefore, the adenosine triphosphate is produced within the matrix of mitochondria and within the stroma of chloroplast. 

In a still later paper " Cohen and McGilvery purified the enzyme further and then found that ATP in the absence of oxidizable metabolite promoted p-aminohippuric acid synthesis anaerobically, that adenosine-monophosphate was active even aerobically only under conditions in which it was phosphorylated to ATP, that AT-phosphoglycine was inactive, as were coenzymes I and II, cocarboxylase, and pyridoxalphosphate. 

Transfer of Phosphate from Phosphocreatine to Glucose—Here phosphocreatine is the donor of phosphate to adenylic acid forming adenosine triphosphate which passes its acid-labile phosphate over to the sugar. The adenylic acid system acts in a catalytic manner as a carrier of phosphate between phosphocreatine and glucose just as it acts catalytically in aerobic phosphorylation as a carrier of inorganic phosphate to the phosphate acceptor. If sufficiently active, adenosinetriphosphatase will interfere with the phosphorylation of the acceptor to a similar extent in both cases. 

Minute spheres, rods, or filaments in the cytoplasm. Mitochondria are the sites of numerous biochemical reactions including amino acid and fatty acid catabolism, the oxidative reactions of the KreE)s cycle, respiratory electron transport, and oxidative phosphorylation. As a result of these reactions, mitochondria are the major producers of the high energy compound adenosine triphosphate (ATP) in aerobically grown cells. 

Glutamic acid is oxidized to completion by the kidney and liver cyclo-phorase suspensions of Green and co-workers (P). The oxidation is associated with aerobic phosphorylation, and requires the presence of adenosine 5 -phosphate (AMP), Mg++, and P. Since aged preparations are stimulated by DPN+ it appears highly probable that cyclophorase preparations contain L-glutamate dehydrogenase and enzymes of the TCA cycle. 

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