Despite the large number of fermentation pathways, only a
few reactions within such pathways are exergonic enough
to conserve energy either by substrate level phosphorylation
or ion-gradient-driven phosphorylation. The latter
contributes only a small fraction to theATPyield of a given
fermentation and, therefore, the ATP yield of a fermentation
usually reflects the amount of ATP synthesized by
substrate level phosphorylation. Enzymes that are coupled
to substrate level phosphorylation are: