According to some of newer sources the ATP yield during aerobic respiration is not 36–38, but only about 30–32 ATP molecules / 1 molecule of glucose , because:
ATP : NADH+H+ and ATP : FADH2 ratios during the oxidative phosphorylation appear to be not 3 and 2, but 2.5 and 1.5 respectively. Unlike in the substrate-level phosphorylation, the stoichiometry here is difficult to establish.
ATP synthase produces 1 ATP / 3 H+. However the exchange of matrix ATP for cytosolic ADP and Pi (antiport with OH− or symport with H+) mediated by ATP–ADP translocase and phosphate carrier consumes 1 H+ / 1 ATP as a result of regeneration of the transmembrane potential changed during this transfer, so the net ratio is 1 ATP : 4 H+.
The mitochondrial electron transport chain proton pump transfers acrosstheinnermembrane10H+ /1NADH+H+ (4+2+4)or6H+ /1FADH2 (2+4).
So the final stoichiometry is 1 NADH+H+ : 10 H+ : 10/4 ATP = 1 NADH+H+ : 2.5 ATP 1 FADH2 : 6 H+ : 6/4 ATP = 1 FADH2 : 1.5 ATP
ATP : NADH+H+ coming from glycolysis ratio during the oxidative phosphorylation is
1.5, as for FADH2, if hydrogen atoms (2H++2e−) are transferred from cytosolic NADH+H+ to mitochondrial FAD by the glycerol phosphate shuttle located in the inner mitochondrial membrane.
2.5 in case of malate-aspartate shuttle transferring hydrogen atoms from cytosolic NADH+H+ to mitochondrial NAD+
So finally we have, per molecule of glucose
Substrate-level phosphorylation: 2 ATP from glycolysis + 2 ATP (directly GTP) from Krebs cycle Oxidative phosphorylation
2 NADH+H+ from glycolysis: 2 × 1.5 ATP (if glycerol phosphate shuttle transfers hydrogen atoms) or 2 × 2.5 ATP (malate-aspartate shuttle)
2 NADH+H+ from the oxidative decarboxylation of pyruvate and 6 from Krebs cycle: 8 × 2.5 ATP 2 FADH2 from the Krebs cycle: 2 × 1.5 ATP
Altogether this gives 4 + 3 (or 5) + 20 + 3 = 30 (or 32) ATP per molecule of glucose
The total ATP yield in ethanol or lactic acid fermentation is only 2 molecules coming from glycolysis, because pyruvate is not transferred to the mitochondrion and finally oxidized to the carbon dioxide (CO2), but reduced to ethanol or lactic acid in the cytoplasm.
References:
Traditionally, the literature has reported (approaching) 36/38 ATP per mole of glucose in aerobic organisms, although they point to the yield of 2.5 and 1.5 ATP for NADH + H + and FADH2, respectively. Therefore, the net balance you have made is the exact one (excellent, by the way), however, this may have some variations facultative or microaerophilic aerobic organisms, such as some intestinal parasites where FAD + is the final acceptor of electron transport in the mmi.
There are literatures that have 36/38 and other 30/32. When I work with my students to produce ATPs per glucose molecule I mention these two possibilities. However, with the value of 38 ATPs, considering 3 ATPs per NADH and 2 ATPs per FADH, I showed the glycolytic pathway and the krebbs and peco cycle for them to reach this quantification of 38 ATPs. I think that regardless of the value, what is interesting is the understanding of the concept.
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