pathways and this provides a useful diagnostic feature in their classifica-
tion (Figure 9.1). Homofermenters produce lactate as virtually a single
product from the fermentation of glucose. They follow the Emden–
Meyerhof–Parnas (EMP) glycolytic pathway whereby the six-carbon
molecule glucose is phosphorylated and isomerized before cleavage by
the enzyme aldolase into glyceraldehyde-3-phosphate. This is then con-
verted to pyruvate during which ATP is produced by substrate-level
phosphorylation at two sites to give an overall yield of two molecules of
ATP for every molecule of glucose fermented. In order to regenerate the
NAD^1 consumed in the oxidation of glyceraldehyde-3-phosphate,
pyruvate is reduced to lactate using NADH.
Heterofermenters produce roughly equimolar amounts of lactate,
ethanol/acetate, and carbon dioxide from glucose. They lack aldolase
and transform the hexose, glucose, into a pentose by a sequence
Figure 9.1 The homo- and heterofermentation pathways
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