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, Theileria and Babesia species possess all the ten enzymes of glycolysis in the genome. Theileria and Babesia 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 and Babesia 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, Babesia 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 BBOV_IV000130
Lactate dehydrogenase 1.1.1.27 BBOV_IV011270
Glycerol-3-phosphate dehydrogenase 1.1.1.8 BBOV_IV004480
Glycerol-3-phosphate dehydrogenase 1.1.5.3 BBOV_III000930
Glyceraldehyde 3-P dehydrogenase 1.2.1.12 BBOV_II002540
Glyceraldehyde 3-P dehydrogenase 1.2.1.12 BBOV_II002540
Hexokinase 2.7.1.1 BBOV_I000860
Hexokinase 2.7.1.1 BBOV_I000860
Phosphofructokinase 2.7.1.11 BBOV_II006170
Glycerol kinase 2.7.1.30 BBOV_I004170
Pyruvate kinase 2.7.1.40 BBOV_III007000
Phosphoglycerate kinase 2.7.2.3 BBOV_IV008070
Acylphosphatase 3.6.1.7 BBOV_IV011650
Fructose bisphosphate aldolase 4.1.2.13 BBOV_IV000790
Enolase 4.2.1.11 BBOV_III007950
Triose phosphate isomerase 5.3.1.1 BBOV_II001220
Phosphoglucose isomerase 5.3.1.9 BBOV_II000240
Phosphoglycerate mutase 5.4.2.1 BBOV_III007860
Hexose transporter none BBOV_IV003170
Hexose transporter none BBOV_IV003170

 

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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