Reaction Process: Reactome:R-TGU-196780
Biotin transport and metabolism related metabolites
find 7 related metabolites which is associated with chemical reaction(pathway) Biotin transport and metabolism
6x(PCCA:PCCB) + ATP + Btn ⟶ 6x(Btn-PCCA:PCCB) + AMP + PPi
Biotin
Biotin (also known as vitamin B7 or vitamin H) is one of the B vitamins.[1][2][3] It is involved in a wide range of metabolic processes, both in humans and in other organisms, primarily related to the utilization of fats, carbohydrates, and amino acids.[4] The name biotin, borrowed from the German Biotin, derives from the Ancient Greek word βίοτος (bíotos; 'life') and the suffix "-in" (a suffix used in chemistry usually to indicate 'forming').[5] Biotin appears as a white, needle-like crystalline solid.[6] Biotin is an organic heterobicyclic compound that consists of 2-oxohexahydro-1H-thieno[3,4-d]imidazole having a valeric acid substituent attached to the tetrahydrothiophene ring. The parent of the class of biotins. It has a role as a prosthetic group, a coenzyme, a nutraceutical, a human metabolite, a Saccharomyces cerevisiae metabolite, an Escherichia coli metabolite, a mouse metabolite, a cofactor and a fundamental metabolite. It is a member of biotins and a vitamin B7. It is a conjugate acid of a biotinate. A water-soluble, enzyme co-factor present in minute amounts in every living cell. It occurs mainly bound to proteins or polypeptides and is abundant in liver, kidney, pancreas, yeast, and milk. Biotin is a metabolite found in or produced by Escherichia coli (strain K12, MG1655). Biotin is a natural product found in Lysinibacillus sphaericus, Aspergillus nidulans, and other organisms with data available. Biotin is hexahydro-2-oxo-1H-thieno(3,4-d)imidazole-4-pentanoic acid. Growth factor present in minute amounts in every living cell. It occurs mainly bound to proteins or polypeptides and is abundant in liver, kidney, pancreas, yeast, and milk. The biotin content of cancerous tissue is higher than that of normal tissue. Biotin is an enzyme co-factor present in minute amounts in every living cell. Biotin is also known as vitamin H or B7 or coenzyme R. It occurs mainly bound to proteins or polypeptides and is abundant in liver, kidney, pancreas, yeast, and milk. Biotin has been recognized as an essential nutrient. Our biotin requirement is fulfilled in part through diet, through endogenous reutilization of biotin and perhaps through capture of biotin generated in the intestinal flora. The utilization of biotin for covalent attachment to carboxylases and its reutilization through the release of carboxylase biotin after proteolytic degradation constitutes the biotin cycle. Biotin deficiency is associated with neurological manifestations, skin rash, hair loss and metabolic disturbances that are thought to relate to the various carboxylase deficiencies (metabolic ketoacidosis with lactic acidosis). It has also been suggested that biotin deficiency is associated with protein malnutrition, and that marginal biotin deficiency in pregnant women may be teratogenic. Biotin acts as a carboxyl carrier in carboxylation reactions. There are four biotin-dependent carboxylases in mammals: those of propionyl-CoA (PCC), 3-methylcrotonyl-CoA (MCC), pyruvate (PC) and acetyl-CoA carboxylases (isoforms ACC-1 and ACC-2). All but ACC-2 are mitochondrial enzymes. The biotin moiety is covalently bound to the epsilon amino group of a Lysine residue in each of these carboxylases in a domain 60-80 amino acids long. The domain is structurally similar among carboxylases from bacteria to mammals. There are four biotin-dependent carboxylases in mammals: those of propionyl-CoA (PCC), 3-methylcrotonyl-CoA (MCC), pyruvate (PC) and acetyl-CoA carboxylases (isoforms ACC-1 and ACC-2). All but ACC-2 are mitochondrial enzymes. The biotin moiety is covalently bound to the epsilon amino group of a Lys residue in each of these carboxylases in a domain 60-80 amino acids long. The domain is structurally similar among carboxylases from bacteria to mammals. Evidence is emerging that biotin participates in processes other than classical carboxylation reactions. Specifically, novel roles for biotin in cell signaling, gene expression, and chromatin structure have been identified in recent years. Human cells accumulate biotin by using both the sodium-dependent multivitamin transporter and monocarboxylate transporter 1. These transporters and other biotin-binding proteins partition biotin to compartments involved in biotin signaling: cytoplasm, mitochondria, and nuclei. The activity of cell signals such as biotinyl-AMP, Sp1 and Sp3, nuclear factor (NF)-kappaB, and receptor tyrosine kinases depends on biotin supply. Consistent with a role for biotin and its catabolites in ... Biotin is an enzyme co-factor present in minute amounts in every living cell. Biotin is also known as coenzyme R and vitamin H or B7. It occurs mainly bound to proteins or polypeptides and is abundant in liver, kidney, pancreas, yeast, and milk. Biotin has been recognized as an essential nutrient. Humans fulfill their biotin requirement through their diet through endogenous reutilization of biotin and perhaps through the capture of biotin generated in the intestinal flora. The utilization of biotin for covalent attachment to carboxylases and its reutilization through the release of carboxylase biotin after proteolytic degradation constitutes the biotin cycle. Biotin deficiency is associated with neurological manifestations, skin rash, hair loss, and metabolic disturbances that are thought to relate to the various carboxylase deficiencies (metabolic ketoacidosis with lactic acidosis). It has also been suggested that biotin deficiency is associated with protein malnutrition, and that marginal biotin deficiency in pregnant women may be teratogenic. Biotin acts as a carboxyl carrier in carboxylation reactions. There are four biotin-dependent carboxylases in mammals: those of propionyl-CoA (PCC), 3-methylcrotonyl-CoA (MCC), pyruvate (PC), and acetyl-CoA carboxylases (isoforms ACC-1 and ACC-2). All but ACC-2 are mitochondrial enzymes. The biotin moiety is covalently bound to the epsilon amino group of a lysine residue in each of these carboxylases in a domain 60-80 amino acids long. The domain is structurally similar among carboxylases from bacteria to mammals. Evidence is emerging that biotin participates in processes other than classical carboxylation reactions. Specifically, novel roles for biotin in cell signalling, gene expression, and chromatin structure have been identified in recent years. Human cells accumulate biotin by using both the sodium-dependent multivitamin transporter and monocarboxylate transporter 1. These transporters and other biotin-binding proteins partition biotin to compartments involved in biotin signalling: cytoplasm, mitochondria, and nuclei. The activity of cell signals such as biotinyl-AMP, Sp1 and Sp3, nuclear factor (NF)-kappaB, and receptor tyrosine kinases depends on biotin supply. Consistent with a role for biotin and its catabolites in modulating these cell signals, greater than 2000 biotin-dependent genes have been identified in various human tissues. Many biotin-dependent gene products play roles in signal transduction and localize to the cell nucleus, consistent with a role for biotin in cell signalling. Posttranscriptional events related to ribosomal activity and protein folding may further contribute to the effects of biotin on gene expression. Finally, research has shown that biotinidase and holocarboxylase synthetase mediate covalent binding of biotin to histones (DNA-binding proteins), affecting chromatin structure; at least seven biotinylation sites have been identified in human histones. Biotinylation of histones appears to play a role in cell proliferation, gene silencing, and the cellular response to DNA repair. Roles for biotin in cell signalling and chromatin structure are consistent with the notion that biotin has a unique significance in cell biology (PMID: 15992684, 16011464). Present in many foods; particularly rich sources include yeast, eggs, liver, certain fish (e.g. mackerel, salmon, sardines), soybeans, cauliflower and cow peas. Dietary supplement. Isolated from various higher plant sources, e.g. sweet corn seedlings and radish leaves An organic heterobicyclic compound that consists of 2-oxohexahydro-1H-thieno[3,4-d]imidazole having a valeric acid substituent attached to the tetrahydrothiophene ring. The parent of the class of biotins. [Raw Data] CB004_Biotin_pos_50eV_CB000006.txt [Raw Data] CB004_Biotin_pos_30eV_CB000006.txt [Raw Data] CB004_Biotin_pos_40eV_CB000006.txt [Raw Data] CB004_Biotin_pos_20eV_CB000006.txt [Raw Data] CB004_Biotin_pos_10eV_CB000006.txt [Raw Data] CB004_Biotin_neg_10eV_000006.txt [Raw Data] CB004_Biotin_neg_20eV_000006.txt Biosynthesis Biotin, synthesized in plants, is essential to plant growth and development.[22] Bacteria also synthesize biotin,[23] and it is thought that bacteria resident in the large intestine may synthesize biotin that is absorbed and utilized by the host organism.[18] Biosynthesis starts from two precursors, alanine and pimeloyl-CoA. These form 7-keto-8-aminopelargonic acid (KAPA). KAPA is transported from plant peroxisomes to mitochondria where it is converted to 7,8-diaminopelargonic acid (DAPA) with the help of the enzyme, BioA. The enzyme dethiobiotin synthetase catalyzes the formation of the ureido ring via a DAPA carbamate activated with ATP, creating dethiobiotin with the help of the enzyme, BioD, which is then converted into biotin which is catalyzed by BioB.[24] The last step is catalyzed by biotin synthase, a radical SAM enzyme. The sulfur is donated by an unusual [2Fe-2S] ferredoxin.[25] Depending on the species of bacteria, Biotin can be synthesized via multiple pathways.[24] Biotin (Vitamin B7) is a water-soluble B vitamin and serves as a coenzyme for five carboxylases in humans, involved in the synthesis of fatty acids, isoleucine, and valine, and in gluconeogenesis. Biotin is necessary for cell growth, the production of fatty acids, and the metabolism of fats and amino acids[1][2][3]. Biotin, vitamin B7 and serves as a coenzyme for five carboxylases in humans, involved in the synthesis of fatty acids, isoleucine, and valine, and in gluconeogenesis. Biotin is necessary for cell growth, the production of fatty acids, and the metabolism of fats and amino acids[1][2][3]. Biotin (Vitamin B7) is a water-soluble B vitamin and serves as a coenzyme for five carboxylases in humans, involved in the synthesis of fatty acids, isoleucine, and valine, and in gluconeogenesis. Biotin is necessary for cell growth, the production of fatty acids, and the metabolism of fats and amino acids[1][2][3].
Adenosine triphosphate
Adenosine triphosphate, also known as atp or atriphos, is a member of the class of compounds known as purine ribonucleoside triphosphates. Purine ribonucleoside triphosphates are purine ribobucleotides with a triphosphate group linked to the ribose moiety. Adenosine triphosphate is slightly soluble (in water) and an extremely strong acidic compound (based on its pKa). Adenosine triphosphate can be found in a number of food items such as lichee, alpine sweetvetch, pecan nut, and black mulberry, which makes adenosine triphosphate a potential biomarker for the consumption of these food products. Adenosine triphosphate can be found primarily in blood, cellular cytoplasm, cerebrospinal fluid (CSF), and saliva, as well as throughout most human tissues. Adenosine triphosphate exists in all living species, ranging from bacteria to humans. In humans, adenosine triphosphate is involved in several metabolic pathways, some of which include phosphatidylethanolamine biosynthesis PE(16:0/18:4(6Z,9Z,12Z,15Z)), carteolol action pathway, phosphatidylethanolamine biosynthesis PE(20:3(5Z,8Z,11Z)/15:0), and carfentanil action pathway. Adenosine triphosphate is also involved in several metabolic disorders, some of which include lysosomal acid lipase deficiency (wolman disease), phosphoenolpyruvate carboxykinase deficiency 1 (PEPCK1), propionic acidemia, and the oncogenic action of d-2-hydroxyglutarate in hydroxygluaricaciduria. Moreover, adenosine triphosphate is found to be associated with rachialgia, neuroinfection, stroke, and subarachnoid hemorrhage. Adenosine triphosphate is a non-carcinogenic (not listed by IARC) potentially toxic compound. Adenosine triphosphate is a drug which is used for nutritional supplementation, also for treating dietary shortage or imbalanc. Adenosine triphosphate (ATP) is a complex organic chemical that participates in many processes. Found in all forms of life, ATP is often referred to as the "molecular unit of currency" of intracellular energy transfer. When consumed in metabolic processes, it converts to either the di- or monophosphates, respectively ADP and AMP. Other processes regenerate ATP such that the human body recycles its own body weight equivalent in ATP each day. It is also a precursor to DNA and RNA . ATP is able to store and transport chemical energy within cells. ATP also plays an important role in the synthesis of nucleic acids. ATP can be produced by various cellular processes, most typically in mitochondria by oxidative phosphorylation under the catalytic influence of ATP synthase. The total quantity of ATP in the human body is about 0.1 mole. The energy used by human cells requires the hydrolysis of 200 to 300 moles of ATP daily. This means that each ATP molecule is recycled 2000 to 3000 times during a single day. ATP cannot be stored, hence its consumption must closely follow its synthesis (DrugBank). Metabolism of organophosphates occurs principally by oxidation, by hydrolysis via esterases and by reaction with glutathione. Demethylation and glucuronidation may also occur. Oxidation of organophosphorus pesticides may result in moderately toxic products. In general, phosphorothioates are not directly toxic but require oxidative metabolism to the proximal toxin. The glutathione transferase reactions produce products that are, in most cases, of low toxicity. Paraoxonase (PON1) is a key enzyme in the metabolism of organophosphates. PON1 can inactivate some organophosphates through hydrolysis. PON1 hydrolyzes the active metabolites in several organophosphates insecticides as well as, nerve agents such as soman, sarin, and VX. The presence of PON1 polymorphisms causes there to be different enzyme levels and catalytic efficiency of this esterase, which in turn suggests that different individuals may be more susceptible to the toxic effect of organophosphate exposure (T3DB). ATP is an adenosine 5-phosphate in which the 5-phosphate is a triphosphate group. It is involved in the transportation of chemical energy during metabolic pathways. It has a role as a nutraceutical, a micronutrient, a fundamental metabolite and a cofactor. It is an adenosine 5-phosphate and a purine ribonucleoside 5-triphosphate. It is a conjugate acid of an ATP(3-). An adenine nucleotide containing three phosphate groups esterified to the sugar moiety. In addition to its crucial roles in metabolism adenosine triphosphate is a neurotransmitter. Adenosine triphosphate is a metabolite found in or produced by Escherichia coli (strain K12, MG1655). Adenosine-5-triphosphate is a natural product found in Chlamydomonas reinhardtii, Arabidopsis thaliana, and other organisms with data available. Adenosine Triphosphate is an adenine nucleotide comprised of three phosphate groups esterified to the sugar moiety, found in all living cells. Adenosine triphosphate is involved in energy production for metabolic processes and RNA synthesis. In addition, this substance acts as a neurotransmitter. In cancer studies, adenosine triphosphate is synthesized to examine its use to decrease weight loss and improve muscle strength. Adenosine triphosphate (ATP) is a nucleotide consisting of a purine base (adenine) attached to the first carbon atom of ribose (a pentose sugar). Three phosphate groups are esterified at the fifth carbon atom of the ribose. ATP is incorporated into nucleic acids by polymerases in the processes of DNA replication and transcription. ATP contributes to cellular energy charge and participates in overall energy balance, maintaining cellular homeostasis. ATP can act as an extracellular signaling molecule via interactions with specific purinergic receptors to mediate a wide variety of processes as diverse as neurotransmission, inflammation, apoptosis, and bone remodelling. Extracellular ATP and its metabolite adenosine have also been shown to exert a variety of effects on nearly every cell type in human skin, and ATP seems to play a direct role in triggering skin inflammatory, regenerative, and fibrotic responses to mechanical injury, an indirect role in melanocyte proliferation and apoptosis, and a complex role in Langerhans cell-directed adaptive immunity. During exercise, intracellular homeostasis depends on the matching of adenosine triphosphate (ATP) supply and ATP demand. Metabolites play a useful role in communicating the extent of ATP demand to the metabolic supply pathways. Effects as different as proliferation or differentiation, chemotaxis, release of cytokines or lysosomal constituents, and generation of reactive oxygen or nitrogen species are elicited upon stimulation of blood cells with extracellular ATP. The increased concentration of adenosine triphosphate (ATP) in erythrocytes from patients with chronic renal failure (CRF) has been observed in many studies but the mechanism leading to these abnormalities still is controversial. (A3367, A3368, A3369, A3370, A3371). Adenosine triphosphate is a metabolite found in or produced by Saccharomyces cerevisiae. An adenine nucleotide containing three phosphate groups esterified to the sugar moiety. In addition to its crucial roles in metabolism adenosine triphosphate is a neurotransmitter. Adenosine triphosphate (ATP) is a nucleotide consisting of a purine base (adenine) attached to the first carbon atom of ribose (a pentose sugar). Three phosphate groups are esterified at the fifth carbon atom of the ribose. ATP is incorporated into nucleic acids by polymerases in the processes of DNA replication and transcription. ATP contributes to cellular energy charge and participates in overall energy balance, maintaining cellular homeostasis. ATP can act as an extracellular signaling molecule via interactions with specific purinergic receptors to mediate a wide variety of processes as diverse as neurotransmission, inflammation, apoptosis, and bone remodelling. Extracellular ATP and its metabolite adenosine have also been shown to exert a variety of effects on nearly every cell type in human skin, and ATP seems to play a direct role in triggering skin inflammatory, regenerative, and fibrotic responses to mechanical injury, an indirect role in melanocyte proliferation and apoptosis, and a complex role in Langerhans cell-directed adaptive immunity. During exercise, intracellular homeostasis depends on the matching of adenosine triphosphate (ATP) supply and ATP demand. Metabolites play a useful role in communicating the extent of ATP demand to the metabolic supply pathways. Effects as different as proliferation or differentiation, chemotaxis, release of cytokines or lysosomal constituents, and generation of reactive oxygen or nitrogen species are elicited upon stimulation of blood cells with extracellular ATP. The increased concentration of adenosine triphosphate (ATP) in erythrocytes from patients with chronic renal failure (CRF) has been observed in many studies but the mechanism leading to these abnormalities still is controversial. (PMID: 15490415, 15129319, 14707763, 14696970, 11157473). 5′-ATP. CAS Common Chemistry. CAS, a division of the American Chemical Society, n.d. https://commonchemistry.cas.org/detail?cas_rn=56-65-5 (retrieved 2024-07-01) (CAS RN: 56-65-5). Licensed under the Attribution-Noncommercial 4.0 International License (CC BY-NC 4.0).
Adenosine monophosphate
Adenosine monophosphate, also known as adenylic acid or amp, is a member of the class of compounds known as purine ribonucleoside monophosphates. Purine ribonucleoside monophosphates are nucleotides consisting of a purine base linked to a ribose to which one monophosphate group is attached. Adenosine monophosphate is slightly soluble (in water) and a moderately acidic compound (based on its pKa). Adenosine monophosphate can be found in a number of food items such as kiwi, taro, alaska wild rhubarb, and skunk currant, which makes adenosine monophosphate a potential biomarker for the consumption of these food products. Adenosine monophosphate can be found primarily in most biofluids, including blood, feces, cerebrospinal fluid (CSF), and urine, as well as throughout all human tissues. Adenosine monophosphate exists in all living species, ranging from bacteria to humans. In humans, adenosine monophosphate is involved in several metabolic pathways, some of which include josamycin action pathway, methacycline action pathway, nevirapine action pathway, and aspartate metabolism. Adenosine monophosphate is also involved in several metabolic disorders, some of which include hyperornithinemia-hyperammonemia-homocitrullinuria [hhh-syndrome], molybdenum cofactor deficiency, xanthinuria type I, and mitochondrial DNA depletion syndrome. Adenosine monophosphate is a drug which is used for nutritional supplementation, also for treating dietary shortage or imbalanc. Adenosine monophosphate, also known as 5-adenylic acid and abbreviated AMP, is a nucleotide that is found in RNA. It is an ester of phosphoric acid with the nucleoside adenosine. AMP consists of the phosphate group, the pentose sugar ribose, and the nucleobase adenine. AMP can be produced during ATP synthesis by the enzyme adenylate kinase. AMP has recently been approved as a Bitter Blocker additive to foodstuffs. When AMP is added to bitter foods or foods with a bitter aftertaste it makes them seem sweeter. This potentially makes lower calorie food products more palatable. [Spectral] AMP (exact mass = 347.06308) and Guanine (exact mass = 151.04941) and 3,4-Dihydroxy-L-phenylalanine (exact mass = 197.06881) and Glutathione disulfide (exact mass = 612.15196) were not completely separated on HPLC under the present analytical conditions as described in AC$XXX. Additionally some of the peaks in this data contains dimers and other unidentified ions. [Spectral] AMP (exact mass = 347.06308) and Glutathione disulfide (exact mass = 612.15196) were not completely separated on HPLC under the present analytical conditions as described in AC$XXX. Additionally some of the peaks in this data contains dimers and other unidentified ions. [Spectral] AMP (exact mass = 347.06308) and Adenine (exact mass = 135.0545) were not completely separated on HPLC under the present analytical conditions as described in AC$XXX. Additionally some of the peaks in this data contains dimers and other unidentified ions. Adenosine monophosphate. CAS Common Chemistry. CAS, a division of the American Chemical Society, n.d. https://commonchemistry.cas.org/detail?cas_rn=67583-85-1 (retrieved 2024-07-01) (CAS RN: 61-19-8). Licensed under the Attribution-Noncommercial 4.0 International License (CC BY-NC 4.0). Adenosine monophosphate is a key cellular metabolite regulating energy homeostasis and signal transduction. Adenosine monophosphate is a key cellular metabolite regulating energy homeostasis and signal transduction. Adenosine monophosphate is a key cellular metabolite regulating energy homeostasis and signal transduction.
Biocytin
C16H28N4O4S (372.18311680000005)
Biocytin is a naturally occurring low molecular weight analog of biotin, and a primary source of this essential metabolite for mammals. Biotinidase acts as a hydrolase by cleaving biocytin and biotinyl-peptides, thereby liberating biotin for reutilization. Mammals cannot synthesize biotin and, therefore, derive the vitamin from dietary sources or from the endogenous turnover of the carboxylases. Free biotin can readily enter the biotin pool, whereas holocarboxylases or other biotin-containing proteins must first be degraded proteolytically to biocytin (biotinyl-e-lysine) or biotinyl-peptides. Biocytin is also an especially versatile marker for neuroanatomical investigations, shown that may have multiple applications, especially for labeling neurons. (PMID: 8930409, 1384763, 2479450) [HMDB] Biocytin is a naturally occurring low molecular weight analog of biotin, and a primary source of this essential metabolite for mammals. Biotinidase acts as a hydrolase by cleaving biocytin and biotinyl-peptides, thereby liberating biotin for reutilization. Mammals cannot synthesize biotin and, therefore, derive the vitamin from dietary sources or from the endogenous turnover of the carboxylases. Free biotin can readily enter the biotin pool, whereas holocarboxylases or other biotin-containing proteins must first be degraded proteolytically to biocytin (biotinyl-e-lysine) or biotinyl-peptides. Biocytin is also an especially versatile marker for neuroanatomical investigations, shown that may have multiple applications, especially for labeling neurons. (PMID:8930409, 1384763, 2479450).
Pyrophosphate
The anion, the salts, and the esters of pyrophosphoric acid are called pyrophosphates. The pyrophosphate anion is abbreviated PPi and is formed by the hydrolysis of ATP into AMP in cells. This hydrolysis is called pyrophosphorolysis. The pyrophosphate anion has the structure P2O74-, and is an acid anhydride of phosphate. It is unstable in aqueous solution and rapidly hydrolyzes into inorganic phosphate. Pyrophosphate is an osteotoxin (arrests bone development) and an arthritogen (promotes arthritis). It is also a metabotoxin (an endogenously produced metabolite that causes adverse health affects at chronically high levels). Chronically high levels of pyrophosphate are associated with hypophosphatasia. Hypophosphatasia (also called deficiency of alkaline phosphatase or phosphoethanolaminuria) is a rare, and sometimes fatal, metabolic bone disease. Hypophosphatasia is associated with a molecular defect in the gene encoding tissue non-specific alkaline phosphatase (TNSALP). TNSALP is an enzyme that is tethered to the outer surface of osteoblasts and chondrocytes. TNSALP hydrolyzes several substances, including inorganic pyrophosphate (PPi) and pyridoxal 5-phosphate (PLP), a major form of vitamin B6. When TSNALP is low, inorganic pyrophosphate (PPi) accumulates outside of cells and inhibits the formation of hydroxyapatite, one of the main components of bone, causing rickets in infants and children and osteomalacia (soft bones) in adults. Vitamin B6 must be dephosphorylated by TNSALP before it can cross the cell membrane. Vitamin B6 deficiency in the brain impairs synthesis of neurotransmitters which can cause seizures. In some cases, a build-up of calcium pyrophosphate dihydrate crystals in the joints can cause pseudogout. COVID info from WikiPathways Corona-virus Coronavirus SARS-CoV-2 COVID-19 SARS-CoV COVID19 SARS2 SARS