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 TP02_0941
Lactate dehydrogenase 1.1.1.27 TP01_1182
Glycerol-3-phosphate dehydrogenase 1.1.1.8 TP01_0302
Glycerol-3-phosphate dehydrogenase 1.1.5.3 TP03_0730
Glyceraldehyde 3-P dehydrogenase 1.2.1.12 TP02_0858
Glyceraldehyde 3-P dehydrogenase 1.2.1.12 TP04_0383
Hexokinase 2.7.1.1 TP01_0043
Hexokinase 2.7.1.1 TP01_0045
Phosphofructokinase 2.7.1.11 TP02_0577
Glycerol kinase 2.7.1.30 TP02_0725
Pyruvate kinase 2.7.1.40 TP04_0607
Phosphoglycerate kinase 2.7.2.3 TP01_0965
Acylphosphatase 3.6.1.7 TP01_1141
Fructose bisphosphate aldolase 4.1.2.13 TP01_0101
Enolase 4.2.1.11 TP04_0700
Triose phosphate isomerase 5.3.1.1 TP04_0464
Phosphoglucose isomerase 5.3.1.9 TP03_0346
Phosphoglycerate mutase 5.4.2.1 TP04_0690
Hexose transporter none TP01_1069
Hexose transporter none TP03_0064
Monocarboxylate transporter none TP03_0374

 

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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