The Embden–Meyerhof–Parnas (EMP) pathway,
which is the most common route and is found in all
major groups of organisms, including filamentous
fungi, yeasts and many bacteria (Fig. 3.1). This pathway
can operate under anaerobic or aerobic conditions and
consists of a sequence of 10 enzyme-catalysed reactions
located within the cytoplasmic matrix. The three key
regulatory enzymes of the pathway (hexokinase, phosphofructokinase
and pyruvate kinase) act irreversibly
(Fig. 3.1). All other steps are freely reversible, which
is important for the biosynthetic role of the pathway
during glucose synthesis (gluconeogenesis, see p. 55).
The irreversible steps have bypasses to enable the pathway
to operate in this anabolic mode.