The original substrate supplies both:
- the oxidized portion that yields energy
- the internally generated electron acceptor needed for redox balance
ATP is generally obtained primarily through substrate-level phosphorylation rather than a conventional respiratory chain using an external terminal acceptor. (PubMed Central (PMC))
Operational definition
Metabolic mode.
Catabolism in which substrate-derived compounds ordinarily serve as both electron donors and electron acceptors, so that redox balance can be restored without requiring an externally supplied respiratory terminal electron acceptor.
ATP is commonly produced largely through substrate-level phosphorylation, although some fermentative organisms also use membrane complexes, ion gradients, or ATP synthase. Fermentation should therefore not be defined solely by the absence of an electron-transport chain.