Glycerol requires 1 ATP per molecule for the conversion into glycerol phosphate. The glycerol phosphate is then converted to dihydroxyacetone phosphate with the production of 1 molecule of NADH. The dihydroxyacetone phosphate can then be oxidized fully to CO2 through glycolysis and the TCA cycle.
In the conversion to pyruvic acid, dihydroxyacetone phosphate generates 1 NADH and 2 ATP molecules per molecule of glycerol. The net effect of converting glycerol to pyruvic acid is −1 ATP + 2 ATP + 2 NADH=1 ATP + 2 NADH=6 ATP, assuming that the NADH are both oxidized with the generation of 2.5 ATP per NADH. The complete oxidation of pyruvate produces 4 NADH, 1 FADH2, and 1 GTP. When the reducing equivalents are oxidized through the electron transport chain, this produces
4 NADH
X 2.5 ATP NADH + 1 FADH2
X 1.5 ATP FADH2 + 1 GTP
X 1 ATP GTP = 12.5 ATP
Each glycerol molecule liberated from a triglyceride thus produces at most 18.5 molecules ATP per molecule glycerol.
Glycerol has a gram molecular weight of 92 g mol
−1. It produces 18.5 moles ATP/92 g mol
−1=0.20 mol g
−1. This is a little more than the energy derived from glucose: 32 moles ATP/180 g/mol=0.18 mol g
−1.
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