<P> The outcome of these transport processes using the proton electrochemical gradient is that more than 3 H are needed to make 1 ATP . Obviously this reduces the theoretical efficiency of the whole process and the likely maximum is closer to 28--30 ATP molecules . In practice the efficiency may be even lower because the inner membrane of the mitochondria is slightly leaky to protons . Other factors may also dissipate the proton gradient creating an apparently leaky mitochondria . An uncoupling protein known as thermogenin is expressed in some cell types and is a channel that can transport protons . When this protein is active in the inner membrane it short circuits the coupling between the electron transport chain and ATP synthesis . The potential energy from the proton gradient is not used to make ATP but generates heat . This is particularly important in brown fat thermogenesis of newborn and hibernating mammals . </P> <P> 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: </P> <Ul> <Li> ATP: NADH + H and ATP: FADH 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 . <Ul> <Li> 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 . </Li> <Li> The mitochondrial electron transport chain proton pump transfers across the inner membrane 10 H / 1 NADH + H (4 + 2 + 4) or 6 H / 1 FADH (2 + 4). </Li> </Ul> </Li> </Ul> <Li> ATP: NADH + H and ATP: FADH 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 . <Ul> <Li> 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 . </Li> <Li> The mitochondrial electron transport chain proton pump transfers across the inner membrane 10 H / 1 NADH + H (4 + 2 + 4) or 6 H / 1 FADH (2 + 4). </Li> </Ul> </Li>

Where do the 38 atp come from in cellular respiration