The fumarate is hydrated to malate by fumarase and exits in exchange for incoming succinate. QH 2 is oxidized by the electron transport chain, reducing 1 to H 2O and driving 6 H + from the matrix to the intermembrane space. During oxidation of succinate to malate by isolated mitochondria, succinate enters on the dicarboxylate carrier in exchange for malate and is oxidized to fumarate by succinate dehydrogenase, reducing Q to QH 2. The values in each column are calculated row-by-row as follows. the maximum P/O ratio for the reactions in column b). Column q expresses this maximum yield of ATP per mol of oxygen atoms consumed ( i.e. Column p gives the maximum total yield of ATP per mol substrate (sum of columns g and o). 1.63 = 1.636363 …) to emphasize that they are not integers or approximations but exact values arising from the arithmetic of small integers as shown (values for glycogen incorporate an assumption about branching, so they are less precise and are therefore rounded to two decimal places). Column o gives ATP ox, the maximum oxidative yield of ATP/mol of substrate oxidized by pyruvate dehydrogenase, TCA cycle, β-oxidation, and electron transport chain, including substrate-linked phosphorylation in the TCA cycle and NADH equivalents imported from glycolytic reactions, and corrected for ATP used to activate substrates other than glucose (calculated using columns b and c and columns h and n).
The maximum net yield of glycolytic ATP/mol of glucose or glycogen converted to pyruvate (and then to lactate or oxidized through the TCA cycle), ATP glyc, is given in column g, after correction for ATP used to activate glucose or glycogen (calculated using columns b and c and columns e and f). A, maximum extramitochondrial ATP yields and P/O ratios. We provide a simple spreadsheet to calculate glycolytic and oxidative ATP production rates from raw extracellular acidification and respiration data.įigure 1 Maximum extramitochondrial ATP yields and P/O ratios for the catabolism of conventional substrates by isolated mammalian mitochondria and physiological substrates by mammalian cells and calculation of the rates of ATP production from glycolysis, tricarboxylic acid cycle, β -oxidation, and oxidative phosphorylation using oxygen consumption rate. Overall, we demonstrate how extracellular fluxes quantitatively reflect intracellular ATP turnover and cellular bioenergetics. Measurement of ATP use revealed no significant preference for glycolytic or oxidative ATP by specific ATP consumers. We illustrate the determination of these indices using C2C12 myoblasts. The Crabtree index and Pasteur index quantify the responses of oxidative and glycolytic ATP production to alterations in glycolysis and oxidative reactions, respectively the supply flexibility index quantifies overall flexibility of ATP supply and the bioenergetic capacity quantifies the maximum rate of total ATP production. Additional indices quantify the acute flexibility of ATP supply. The Warburg effect is a chronic increase in glycolytic index, quantified by the Warburg index. The glycolytic index reports the proportion of ATP production from glycolysis and identifies cells as primarily glycolytic (glycolytic index > 50%) or primarily oxidative. We introduce novel indices to quantify bioenergetic phenotypes. Complete oxidation of glucose by cells yields up to 33.45 ATP/glucose with a maximum P/O of 2.79.
Mitochondrial P/O ratios (mol of ATP generated per mol of consumed) are 2.73 for oxidation of pyruvate plus malate and 1.64 for oxidation of succinate. We update theoretical maximum ATP yields by mitochondria and cells catabolizing different substrates. We describe here how rates of ATP generation by each pathway can be calculated from simultaneous measurements of extracellular acidification and oxygen consumption. Partitioning of ATP generation between glycolysis and oxidative phosphorylation is central to cellular bioenergetics but cumbersome to measure. Glycobiology and Extracellular Matrices.
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