And an incomplete list of unexpected CO₂ sources:
Process
Enzyme
Reaction
Pentose Phosphate Pathway
PGDH
Hexose (6C) → pentose (5C) +
CO₂ (1C)
Fatty acid synthesis
KAS*
Malonyl (3C) + acetyl (2C) → ketobutyryl (4C) +
CO₂ (1C)
Acetone synthesis
-
Acetoacetate (4C) → acetone (3C) +
CO₂ (1C)
Oxoglutarate oxygenases
OGO
Oxoglutarate (5C) → succinate (4C) +
CO₂ (1C)
Pyruvate synthesis from malate
ME
Malate (4C) → pyruvate (3C) +
CO₂ (1C)
PEP synthesis
PEPCK
Oxaloacetate (4C) → pyruvate-enol-phosphate (3C) +
CO₂ (1C)
Glycine cleavage system
GLDC
Glycine (2C) + THF (+0C) →→ methylene-THF (+1C) +
CO₂ (1C)
Coenzime A synthesis
PPCD
PPC (12C) → P4P (11C) +
CO₂ (1C)
Aldehyde dehydrogenase
ALDH
formyl-THF (+1C) → THF (+0C) +
CO₂ (1C)
Taurine synthesis
CSAD
CSA/CA (3C) → hTau/Tau (2C) +
CO₂ (1C)
Cholesterol synthesis
PPMD
Mevalonate-5-diphosphate (6C) → Isopentenyl diphosphate (5C) +
CO₂ (1C)
Polyamine synthesis
SAMD
SAM (–0C) → dcSAM (–1C) +
CO₂ (1C)
Other biogenic amine syntheses (AA decarboxylations)
†
*Preceded by carbon incorporation: gain followed by loss. But remains a reaction that releases carbon dioxide.
†Biochemical and Pharmacological Properties of Biogenic Amines
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