Redox metabolism

Redox metabolism is an important metabolic pathway in all apicomplexans. This pathway shows the series of oxidation/reduction activities involved in removal of oxidative radicals such as superoxide anions, hydrogen peroxide and other toxic nucleophiles produced from different metabolic reactions. These reactive oxygen species cause oxidative damage to DNA, lipids and proteins. There are several antioxidant systems present in cells to protect them from these damages. This includes enzymes such as superoxide dismutase which reduces superoxide anion to H2O2 and catalase which reduces H2O2 to water and oxygen. The enzyme peroxiredoxin also reduces H2O2. The oxidised peroxiredoxin can be reduced back by thiols such as glutathione and thioredoxin. The glutathione system consists of glutathione and the enzymes glutathione peroxidase, glutathione reductase and glutathione S-transferase [1]. Glutathione is a tripeptide of glutamine-cysteine-glycine and synthesised de novo in two reactions steps. This glutathione synthesis is also included in this pathway. Glutathione synthase is present in Plasmodium falciparum and Toxoplasma gondii and absent in Cryptosporidium species. Glutathione peroxidase and glutathione S-transferase catalyse reduction of oxidative radicals by oxidising glutathione. Glutathione can be reduced back by glutathione reductase [1]. Another redox protein thioredoxin is important in reduction of ribonucleotides to deoxyribonucleotides and its partner thioredoxin reductase catalyses reduction of oxidised thioredoxin using NADPH as electron donor. Catalase and gamma-glutamylcysteine synthetase are the other enzymes present in P. falciparum and T. gondii and absent in Cryptosporidium species.

 

Enzyme EC Number Gene id
Peroxiredoxin 1.11.1.15 CMU_012880
Peroxiredoxin 1.11.1.15 CMU_034200
Glutathione peroxidase 1.11.1.9 CMU_038280
Superoxide dismutase (Fe) 1.15.1.1 CMU_015930
Ribonucleotide reductase 1.17.4.1 CMU_007940
Ribonucleotide reductase 1.17.4.1 CMU_027540
Thioredoxin reductase 1.8.1.9 CMU_002600
Glutathione S-transferase 2.5.1.18 CMU_014950
Thioredoxin none CMU_000950
Thioredoxin none CMU_005950
Glutaredoxin none CMU_016150
Thioredoxin none CMU_019940
Thioredoxin none CMU_023150
Thioredoxin none CMU_031740
Thioredoxin none CMU_032380
Glutaredoxin none CMU_037450
Thioredoxin none CMU_041260