Glycolysis

Glycolysis (glycose+lysis= breaking of glucose) is a sequence of 10 definite reactions which leads to breaking of glucose into pyruvate. This is the first of four steps of aerobic respiration. This cytosolic metabolic pathway produces a net gain of 2 ATPs. This step is also common to anaerobic respiration as it does not require O2. In anaerobic respiration, pyruvate will then be converted to lactate (e.g. skeletal musles) or ethanol and carbon dioxide (e.g. yeast) to re-oxidise electron carrier NADH to provide NAD+ for glycolysis.

 

The apicomplexans Toxoplasma gondii, Plasmodium falciparum and Theileria species possess all the ten enzymes of glycolysis in the genome. Cryptosporidium and Theileria species possess one lactate dehydrogenase enzyme (converts pyruvate to lactate) as in P. falciparum , whereas T. gondii possesses 2 lactate dehydrogenase isoforms. Both NAD-dependent glycerol-3-phosphate dehydrogenase and FAD-dependent glycerol-3-phophate dehydrogenase (catalyse bidirectional conversion of glycerol-3-phosphate to glycerone phosphate) are present in Theileria as in glycolysis pathway for T. gondii. The enzymes such as aldehyde reductase, glycerol kinase and acylphosphatase are added to the pathway here. In addition, gluconeogenesis enzyme, fructose bisphosphatase present in T. gondii is absent in other apicomplexans including Cryptosporidium, Theileria and Plasmodium species.

 

The enzymatic activities of glycolytic enzymes such as hexokinase, glucose phosphate isomerase, phosphofructokinase, fructose bisphosphate aldolase, phosphoglycerate kinase, enolase, pyruvate kinase, lactate dehydrogenase, glycerol-3-phosphate dehydrogenase (1.1.1.8) and glycerol kinase were measured by Kiama et al to assess the significance of glycolysis pathway in Theileria parva schizonts. This showed the enzymatic activities of glycerol kinase and glycerol-3-phoshate dehydrogenase are about 16 times lower than the other enzymes. These results suggest the presence of functional glycolytic pathway and low levels of glycerol catabolism in T. parva schizonts [1]. The activity of glyceraldehyde 3-phosphate dehydrogenase had been detected in both piroplasma and schizont stages about three decades ago [2]. These evidence suggest that Theileria mainly depends on glycolysis for energy generation as P. falciparum.

 

Enzyme EC Number Gene id
Aldehyde reductase 1.1.1.21 TA15960
Lactate dehydrogenase 1.1.1.27 TA09590
Glycerol-3-phosphate dehydrogenase 1.1.1.8 TA21330
Glycerol-3-phosphate dehydrogenase 1.1.5.3 TA17925
Glyceraldehyde 3-P dehydrogenase 1.2.1.12 TA08145
Glyceraldehyde 3-P dehydrogenase 1.2.1.12 TA15530
Hexokinase 2.7.1.1 TA19800
Hexokinase 2.7.1.1 TA19810
Phosphofructokinase 2.7.1.11 TA13950
Glycerol kinase 2.7.1.30 TA14775
Pyruvate kinase 2.7.1.40 TA10915
Phosphoglycerate kinase 2.7.2.3 TA06655
Acylphosphatase 3.6.1.7 TA16545
Fructose bisphosphate aldolase 4.1.2.13 TA20060
Enolase 4.2.1.11 TA10425
Triose phosphate isomerase 5.3.1.1 TA08590
Phosphoglucose isomerase 5.3.1.9 TA04045
Phosphoglycerate mutase 5.4.2.1 TA10465
Hexose transporter none TA02480
Hexose transporter none TA02485
Monocarboxylate transporter none TA04195

 

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Sources and fates of metabolites

 

Substrate Source pathways Product Fate pathways
alpha-D-Glucose Host alpha-D-Glucose-6P Pentose phosphate cycle
    alpha-D-Glucose-1P Pyrimidine metabolism
    beta-D-Fructose-6P Aminosugars metabolism
    Phosphoenolpyruvate Pyruvate metabolism
    sn-glycerol-3P Phosphatidylethanolamine metabolism
    Glyceraldehyde Host?
    Lactate Host