Carbohydrate and energy metabolism in trypanosome and plasmodia
CARBOHYDRATE AND ENERGY
METABOLISM IN TRYPANOSOME AND
ASARE, KUMI KWAME
Trypanosomes go through a complex life cycle
involving vertebrate host and a vector tsetse
Vertebrate host comprising long slender,
intermediate and short stumpy form.
Vector phase comprising procyclic
trypomastigote, epimestigote and metacyclic
T. brucei actively catabolize glucose, fructose,
mannose and glycerol.
Long slender form lack mitochondral TCA and
functional respiratory chain.
Short stumpy stages is able to utilize alpha
ketoglutarate, glucose, fructose and glycerol.
Blood stream form do not store energy
The long slender forms metabolize glucose to
pyruvate with trace amount CO2 and sometimes
Lack lactate dehydrogenase, pyruvate
Short stumpy form contain mitochondra and
produce pyruvate, glycerol, acetate, succinate
and co2 .
Reoxidation of NADH in the glycosome is
dehydrogenase and mitochondrial FAD-linked
The terminal oxidase reduce molecular oxygen
Mitochondrial glycerol-3-phosphate oxidase is
inhibited with salicyl hydroxamic acid (SHAM).
Long slender forms continue to utilize glucose by
G3P-DHAP which prevent glycerol-3-phosphate.
Glycosomal ATP is trapped by the
phosphorylation of glucose.
Anaerobiosis leads to high glycerol-3-phosphate
and ADP with decrease ATP cause glycerol-3-
phosphate to diffuse out.
Causing reversal of glycerol kinase action to form
ATP from glycerol-3-phosphate and ADP.
In anaerobic condition glucose form equimolar
amounts of pyruvate and glycerol with a net ATP
Cells survive and remain motile under anaerobic
condition with decrease ATP.
Glycerol can not serve as substrate because G3P
can not be oxidized to DHAP without molecular
Procyclic form metabolize glucose, fructose,
mannose and glycerol to produce acetate,
succinate, alanine, alpha ketoglutarate and CO2.
Under anaerobic condition utilize glucose and
glycerol and produce CO2 in a form of succinate
Glycosomal phosphoenolpyruvate carboxykinase
and malate dehydrogenase is present in procyclic
Erythrocytic stages of the malaria parasite do not
Utilization of glucose increase to about 50-100
In infected red cells with P. falciparum utilize
glucose in anaerobic glycolysis to lactic acid.
Both the parasite and the host lack TCA cycle.
However, Avian malaria parasite under TCA cycle
with the presence of enzymes isocitrate
dehydrogenase and succinate dehydrogenase.
There is the presence malate dehydrogenase
in both mammalian parasite and avian
parasite but appears to cytosolic.
Although intraerythrocytic stages depend
mainly on glycolysis but mitochondria function
influence the parasite survival.
They are capable of oxidizing NADH, glycerol-
3-phosphate and succinate.
Mitochondria of P. falciparum oxidize
NADH-fumarate reductase involved in the
reoxidation of mitochondrial NADH.
P. falciparum has a complete set of glycolytic
enzyme which is high in the infected cells.
Several non-glycolytic enzymes such as
diphosphoglycerate mutase and adenylate
kinase decreased in activity.
Most of the enzymes except for glucose-6-
phosphate dehydrogenase can be obtain from
the parasite after lysis.
The pathway for the synthesis of 2,3-
diphosphoglycerate is absent.