Table 1.

Energetics of the conversion reactions for major classes of biological macromolecules under anaerobic, aerobic, and micro-aerobic conditions

Model substrate		Reaction under aerobic/micro-aerobic conditions	ΔG0′a kJ react.−1	ΔG′b kJ react.−1
Proteins	Creatine	C4H9N3O2 + 3 O2 → 4 CO2 + 3 NH3	− 1392.9	− 1299.3
Carbohydrates	Sucrose	C12H22O11 + 12 O2 → 12 CO2 + 11 H2O	− 5789.4	− 5415.2
Lipids	Oleatec	C18H33O2− + H+ + 25.5 O2 → 18 CO2 + 17 H2O	− 10,916.1	− 10,120.9
Hydrocarbons	Benzenec	C6H6 + 7.5 O2 → 6 CO2 + 3 H2O	− 3202.2	− 2941.6
Hydrocarbons	Toluenec	C7H8 + 9 O2 → 7 CO2 + 4 H2O	− 3823.5	− 3509.0
Intermediary products
Amino acids	Alanine	C3H7NO2 + 3 O2 → 3 CO2 + NH3 + 2 H2O	− 1312.5	− 1210.7
Amino acids	Glycine	C2H5NO2 + 1.5 O2 → 2 CO2 + NH3 + H2O	− 681.7	− 631.5
Amino acids	Leucine	C6H13NO2 + 7.5 O2 → 6 CO2 + NH3 + 5 H2O	− 3234.7	− 3181.9
Monosaccharides	Glucose	C6H12O6 + 6 O2 → 6 CO2 + 6 H2O	− 2872.0	− 2658.2
Alcohols	Ethanol	C2H5OH + 3 O2 → 2 CO2 + 3 H2O	− 1318.5	− 1221.5
VFA	Butyrate	C4H7O2− + H+ + 5 O2 → 4 CO2 + 4 H2O	− 2133.7	− 1964.0
VFA	Propionate	C3H5O2− + H+ + 3.5 O2 → 3 CO2 + 3 H2O	− 1493.7	− 1376.3
VFA	Acetate	C2H3O2− + H+ + 2 O2 → 2 CO2 + 2 H2O	− 853.8	− 788.0
−	H2	H2 + 0.5 O2 → H2O	− 237.2	− 221.6
Model substrate		Reaction under anaerobic (methanogenic) conditions	ΔG0′a kJ react.−1	−
Proteins	Creatine	C4H9N3O2 + 3 H2O → 1.5 CH4 + 2.5 CO2 + 3 NH3	− 165.9	−
Carbohydrates	Sucrose	C12H22O11 + H2O → 6 CH4 + 6 CO2	− 881.6	−
Lipids	Oleatec	C18H33O2 + H+ + 8.5 H2O → 12.75 CH4 + 5.25 CO2	− 527.0	−
Hydrocarbons	Benzenec	C6H6 + 4.5 H2O → 3.75 CH4 + 2.25 CO2	− 134.8	−
Hydrocarbons	Toluenec	C7H8 + 5 H2O → 4.5 CH4 + 2.5 CO2	− 142.6	−
Intermediary products
Amino acids	Alanine	C3H7NO2 + H2O → 1.5 CH4 + 1.5 CO2 + NH3	− 85.5	−
Amino acids	Glycine	C2H5NO2 + 0.5 H2O → 0.75 CH4 + 1.25 CO2 + NH3	− 68.2	−
Amino acids	Leucine	C6H13NO2 + 2.5 H2O → 3.75 CH4 + 2.25 CO2 + NH3	− 167.4	−
Monosaccharides	Glucose	C6H12O6 → 3 CH4 + 3 CO2	− 418.1	−
Alcohols	Ethanol	C2H5OH → 1.5 CH4 + 0.5 CO2	− 91.6	−
VFA	Butyrate	C4H7O2− + H+ + H2O → 2.5 CH4 + 1.5 CO2	− 88.7	−
VFA	Propionate	C3H5O2− + H+ + 0.5 H2O → 1.75 CH4 + 1.25 CO2	− 62.2	−
VFA	Acetate	C2H3O2− + H+ → CO4 + CO2	− 35.8	−
−	H2	H2 + 0.25 CO2 → 0.25 CH4 + 0.5 H2O	− 32.7	−

^aGibbs free energy change (ΔG^0′) was calculated under standard conditions (25 °C, solute concentrations of 1 mol L⁻¹, gas partial pressure of 1 atm, and H⁺ concentration at pH 7). Data obtained or calculated from Thauer et al. (1977)

^bΔG′ was calculated with solute concentrations of 1 mol L⁻¹, oxygen concentration of 3.41 µmol L⁻¹ (equivalent to 1% air-saturated water at sea level (1 atm) and 4 °C), gas partial pressure of 1 atm, pH 7, at 25 °C

^cRepresentative of toxic compounds