The pyruvate formed is reduced to lactate by the action of
lactate dehydrogenase, which catalyses a stereospecific
reduction to either l- or d-lactate. The ATP yield is 2 mol
per mol glucose. Heterofermentative bacteria are devoid of
aldolase but contain phosphoketolase instead. Glucose 6-
phosphate is oxidized to 6-phosphogluconate and then
decarboxylated to ribulose 5-phosphate. After epimerization
the xylulose 5-phosphate is split by phosphoketolase
to acetyl phosphate and glyceraldehyde 3-phosphate. To
maintain a proper redox balance acetyl-CoA derived from
acetyl phosphate is reduced to ethanol, and the glyceraldehyde
3-phosphate is converted to lactate. The overall
reaction