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 cgd4_740
Glutathione peroxidase 1.11.1.9 cgd3_460
Superoxide dismutase (Fe) 1.15.1.1 cgd5_3230
Ribonucleotide reductase 1.17.4.1 cgd6_1950
Ribonucleotide reductase 1.17.4.1 cgd6_690
Thioredoxin reductase 1.8.1.9 cgd2_4320
Glutathione S-transferase 2.5.1.18 cgd7_4780
Thioredoxin none cgd1_3660
Glutaredoxin none cgd2_2540
Thioredoxin none cgd3_2500
Thioredoxin none cgd4_1650
Thioredoxin none cgd5_660
Glutaredoxin none cgd6_3970
Thioredoxin none cgd7_3170
Thioredoxin none cgd8_3690