trans

STEPS OF AMITOCHONDRIATE CORE METABOLISM 131
G. intestinalis E. histolytica
P-enolpyruvate
ADP
AMP
[10]
GDP GTP
Oxalacetate P-enolpyruvate
[12]
PP
PP i
AMP i
[11] CO 2
[14] [11]
P i
[14]
CO 2
Oxalacetate
[14]
ATP
ATP
P i
ATP
P i
Pyruvate
[15]
Malate
Pyruvate
[15]
Malate
Pyruvate
[16]
CO 2 CoA
Acetyl-CoA
Acetate
2 Fd
[17]
2 Fd
ADP
[18]
ATP
[19]
CoA
Aminoacid
-Ketoacid
CoA
Alanine [Acetaldehyde] Ethanol
[19]
CELL MEMBRANE
Acetate
Ethanol
Alanine
FIGURE 7.2 Map of the extensions of glycolysis beyond phosphoenolpyruvate in Type I amitochondriate parasites:
G. intestinalis (left) and E. histolytica (right). Fate of reducing equivalents omitted. Metabolic end-products boxed.
[10] pyruvate kinase, [11] pyruvate, orthophosphate dikinase, [12] phosphoenolpyruvate carboxykinase (GTPdependent),
[13] phosphoenolpyruvate carboxytransferase (PP i -dependent), [14] malate dehydrogenase, [15]
decarboxylating malate dehydrogenase (malic enzyme), [16] pyruvate aminotransferase, [17] pyruvate:ferredoxin
oxidoreductase, [18] acetyl-CoA synthetase (ADP-forming), [19] aldehyde/alcohol dehydrogenase, [Fd] ferredoxin.
production presupposes the presence of a so
far elusive ferredoxin:NAD oxidoreductase.
The two trichomonad species belong to Type
II amitochondriates characterized by a hydrogenosomal/cytosolic
compartmentalization of
metabolism (Figure 7.3). Glycolysis through
the formation of pyruvate (or malate) is
cytosolic, as is the production of all metabolic
end-products (lactate [reaction 25], ethanol
[reactions 23 and 24], alanine [reaction 16] and
BIOCHEMISTRY AND CELL BIOLOGY: PROTOZOA