Table 1 Changes of free energy (ΔG0′; pH = 7, T = 298 K) for each AOB metabolic reaction

From: Back flux during anaerobic oxidation of butane supports archaea-mediated alkanogenesis

Index

Reactiona

ΔG0′ (kJ mol−1)

Stoi.c

Enzymed

Ex = −0.414Ve

Ex = −0.22Vf

1

C4H10 (g) +  CoM-S-S-CoB == C4H9-S-CoM + HS-CoB

16.900

1

ACR

16.900

16.900

2

HS-CoM + HS-CoB + 2Fdred + 2H+ + 2F420 == CoM-S-S-CoB + 2Fdox + 2F420H2

7.141

1

Hdr-FrhB

7.141

7.141

3

C4H9-S-CoM + CoA + H2O + 2X == Butyryl-CoA + HS-CoM + 2XH2

Related to Exb

1

?

104.003

29.119

4

Butyryl-CoA + 2NAD+ + 2Fdred == Crotonyl-CoA + 2NADH + 2Fdox

25.090

1

Bcd-Etf

25.090

25.090

5

Crotonyl-CoA + H2O == (S)-3-Hydroxybutyryl-CoA

0.300

1

Ech

0.300

0.300

6

(S)-3-Hydroxybutyryl-CoA + NAD+ == Acetoacetyl-CoA + NADH + H+

12.545

1

HADH

12.545

12.545

7

Acetoacetyl-CoA + CoA == 2 Acetyl-CoA

−28.100

1

ACAT

−28.100

−28.100

8

NADH + H+ + MQ == NAD+ + MQH2

−46.320

5

NDH

−46.320

−46.320

9

Acetyl-CoA + H4MPT + 2 Fdox + H2O == CH3-H4MPT + CoA + CO2 (g) + 2 Fdred + 2H+

66.114

2

ACS-CODH

66.114

66.114

10

CH3-H4MPT + NAD+ == CH2 = H4MPT + NADH + H+

1.140

2

Met

1.140

1.140

11

CH2 = H4MPT + F420 + H+ == CH ≡ H4MPT+ + F420H2

−6.500g

2

Mtd

−6.500

−6.500

12

CH ≡ H4MPT+ + H2O == HCO-H4MPT + H+

2.000g

2

Mch

2.000

2.000

13

HCO-H4MPT + MF == HCO-MF + H4MPT

−21.100g

2

Ftr

−21.100

−21.100

14

HCO-MF + H2O + 2Fdox == CO2 (g) + MF + 2H+ + 2Fdred

0.598

2

Fwd

0.598

0.598

15

F420H2 + MQ == F420 + MQH2

−50.180

4

Fqo

−50.180

−50.180

16

2 Fdred + 2H+ + MQ == 2 Fdox + MQH2

−81.060

2

Nuo

−81.060

−81.060

17

MQH2 + X == MQ + XH2

Related to Exb

11

? MHCs

64.462

27.020

  1. aX and XH2 refer to the oxidized and reduced forms of the unknown electron carrier between butane oxidizing archaea and sulfate-reducing bacteria. Similarly, MQ and MQH2 refer to the oxidized and reduced forms of menaquinone.
  2. bThe ΔG0 of reactions 3 and 17 is −386Ex – 55.801 and −193Ex – 15.440 kJ mol−1, respectively. Ex: redox potential of the unknown electron carrier X under biological standard condition (unit: V).
  3. cStoichiometry of each individual reaction step during AOB; the sum of all reactions is the net AOB C4H10 + 13X → 4CO2 + 13XH2.
  4. dACR alkyl-coenzyme M reductase, Hdr heterodisulfide reductase, FrhB F420 hydrogenase subunit B, Bcd butyryl CoA dehydrogenase, EtfAB electron transfer proteins, Ech Enoyl-CoA hydratase, HADH 3-Hydroxyacyl-CoA dehydrogenase, ACAT Acetyl-CoA acetyltransferase, NDH NADH dehydrogenase (non-electrogenic), ACS acetyl-CoA synthase, CODH CO dehydrogenase, Met: methyl-methanotetrahydropterin (H4MPT) dehydrogenase, Mch N5,N10-methenylH4MPT cyclohydrolase, Ftr FormylMF-H4MPT formyltransferase, Fwd Formylmethanofuran dehydrogenase, Fqo F420H2:quinone oxidoreductase, Nuo-like NADH:quinone oxidoreductase, MHCs multiheme-cyctochrome c.
  5. eStandard Gibbs free energy change for each reaction step assuming Ex is equivalent to the standard redox potential of H2/H+.
  6. fStandard Gibbs free energy change for each reaction step assuming Ex is equivalent to the average redox potential of sulfate reduction.
  7. g ΔG0′ of the reaction is gather from Blaut et al.79; ΔG0′ of the remaining reactions are calculated from standard redox potential or estimated using Equilibrator (Supplementary Data).