Browsing Compounds

One-methylhistidine (1-MHis) is derived mainly from the anserine of dietary flesh sources, especially poultry. The enzyme, carnosinase, splits anserine into b-alanine and 1-MHis. High levels of 1-MHis tend to inhibit the enzyme carnosinase and increase anserine levels. Conversely, genetic variants with deficient carnosinase activity in plasma show increased 1-MHis excretions when they consume a high meat diet. Reduced serum carnosinase activity is also found in patients with Parkinson's disease and multiple sclerosis and patients following a cerebrovascular accident. Vitamin E deficiency can lead to 1-methylhistidinuria from increased oxidative effects in skeletal muscle.

1,3-Diaminopropane is a stable, flammable and highly hydroscopic fluid. It is a polyamine that is normally quite toxic if swallowed, inhaled or absorbed through the skin. It is a catabolic byproduct of spermidine. It is also a precursor in the enzymatic synthesis of beta-alanine. 1, 3-Diaminopropane is involved in the arginine/proline metabolic pathways and the beta-alanine metabolic pathway.

2-Ketobutyric acid is a substance that is involved in the metabolism of many amino acids (glycine, methionine, valine, leucine, serine, threonine, isoleucine) as well as propanoate metabolism and C-5 branched dibasic acid metabolism. More specifically, alpha-ketobutyric acid is a product of the lysis of cystathionine. It is also one of the degradation products of threonine. It can be converted into propionyl-CoA (and subsequently methylmalonyl CoA, which can be converted into succinyl CoA, a citric acid cycle intermediate), and thus enter the citric acid cycle.

2-Hydroxybutyric acid (alpha-hydroxybutyrate) is an organic acid derived from alpha-ketobutyrate. alpha-Ketobutyrate is produced by amino acid catabolism (threonine and methionine) and glutathione anabolism (cysteine formation pathway) and is metabolized to propionyl-CoA and carbon dioxide (PMID: 20526369). 2-Hydroxybutyric acid is formed as a by-product of the formation of alpha-ketobutyrate via a reaction catalyzed by lactate dehydrogenase (LDH) or alpha-hydroxybutyrate dehydrogenase (alphaHBDH). alpha-Hydroxybutyric acid is primarily produced in mammalian hepatic tissues that catabolize L-threonine or synthesize glutathione. Oxidative stress or detoxification of xenobiotics in the liver can dramatically increase the rate of hepatic glutathione synthesis. Under such metabolic stress conditions, supplies of L-cysteine for glutathione synthesis become limiting, so homocysteine is diverted from the transmethylation pathway (which forms methionine) into the transsulfuration pathway (which forms cystathionine). 2-Hydroxybutyrate is released as a byproduct when cystathionine is cleaved into cysteine that is incorporated into glutathione. Chronic shifts in the rate of glutathione synthesis may be reflected by urinary excretion of 2-hydroxybutyrate. 2-Hydroxybutyrate is an early marker for both insulin resistance and impaired glucose regulation that appears to arise due to increased lipid oxidation and oxidative stress (PMID: 20526369). 2-Hydroxybutyric acid is often found in the urine of patients suffering from lactic acidosis and ketoacidosis. 2-Hydroxybutyric acid generally appears at high concentrations in situations related to deficient energy metabolism (e.g. birth asphyxia) and also in inherited metabolic diseases affecting the central nervous system during neonatal development, such as "cerebral" lactic acidosis, glutaric aciduria type II, dihydrolipoyl dehydrogenase (E3) deficiency, and propionic acidemia. More recently it has been noted that elevated levels of alpha-hydroxybutyrate in the plasma is a good marker for early-stage type II diabetes (PMID: 19166731). It was concluded from studies done in the mid-1970's that an increased NADH2/NAD ratio was the most important factor for the production of 2-hydroxybutyric acid (PMID: 168632).

2-Methoxyestrone is a steroid derivative that is a byproduct of estrone and 2-hydroxyestrone metabolism. It is part of the androgen and estrogen metabolic pathway. The acid ionization constant (pKa) of 2-methoxyestrone is 10.81 (PMID: 516114). 2-Methoxyestrone can be metabolized to a sulfated derivative (2-methoxyestrone 3-sulfate) via steroid sulfotransferase (EC 2.8.2.15). It can also be glucuronidated to 2-methoxyestrone 3-glucuronide by UDP glucuronosyltransferase (EC 2.4.1.17).

(R)-3-Hydroxybutyric acid is a butyric acid substituted with a hydroxyl group in the beta or 3 position. 3-hydroxybutyric acid, or beta-hydroxybutyrate, is involved in the synthesis and degradation of ketone bodies. Like the other ketone bodies (acetoacetate and acetone), levels of beta-hydroxybutyrate are raised in the blood and urine in ketosis. Beta-hydroxybutyrate is a typical partial-degradation product of branched-chain amino acids (primarily valine) released from muscle for hepatic and renal gluconeogenesis This acid is metabolized by 3-hydroxybutyrate dehydrogenase (catalyzes the oxidation of D-3-hydroxybutyrate to form acetoacetate, using NAD+ as an electron acceptor). The enzyme functions in nervous tissues and muscles, enabling the use of circulating hydroxybutyrate as a fuel. In the liver mitochondrial matrix, the enzyme can also catalyze the reverse reaction, a step in ketogenesis. 3-Hydroxybutyric acid is a chiral compound having two enantiomers, D-3-hydroxybutyric acid and L-3-hydroxybutyric acid. In humans, beta-hydroxybutyrate is synthesized in the liver from acetyl-CoA, and can be used as an energy source by the brain when blood glucose is low. It can also be used for the synthesis of biodegradable plastics (Wikipedia).

2'-Deoxyuridine is a naturally occurring nucleoside. It is similar in chemical structure to uridine, but without the 2'-hydroxyl group. It is considered to be an antimetabolite that is converted to deoxyuridine triphosphate during DNA synthesis. Laboratory suppression of deoxyuridine is used to diagnose megaloblastic anemia due to vitamin B12 and folate deficiencies.

One of the principal nucleosides of DNA composed of cytosine and deoxyribose. A nucleoside consists of only a pentose sugar linked to a purine or pyrimidine base, without a phosphate group. When N1 is linked to the C1 of deoxyribose, deoxynucleosides and nucleotides are formed from cytosine and deoxyribose; deoxycytidine monophosphate (dCMP), deoxycytidine diphosphate (dCDP), deoxycytidine triphosphate (dCTP). CTP is the source of the cytidine in RNA (ribonucleic acid) and deoxycytidine triphosphate (dCTP) is the source of the deoxycytidine in DNA (deoxyribonucleic acid).

Cortexolone is the precursor of cortisol. Accumulation of cortexolone can happen in a defect known as congenital adrenal hyperplasia, which is due to 11-beta-hydroxylase deficiency, resulting in androgen excess, virilization, and hypertension (PMID: 2022736). Cortexolone is a 17-hydroxycorticosteroid with glucocorticoid and anti-inflammatory activities (PubChem).

11-Deoxycorticosterone (also called desoxycortone, 21-hydroxyprogesterone, DOC, or simply deoxycorticosterone) is a steroid hormone produced by the adrenal gland that possesses mineralocorticoid activity and acts as a precursor to aldosterone. It is classified as a member of the 21-hydroxysteroids. 21-hydroxysteroids are steroids carrying a hydroxyl group at the 21-position of the steroid backbone. Deoxycorticosterone is very hydrophobic, practically insoluble (in water), and relatively neutral. Deoxycorticosterone can be synthesized from progesterone by 21-beta-hydroxylase and is then converted to corticosterone by 11-beta-hydroxylase. Corticosterone is then converted to aldosterone by aldosterone synthase. Deoxycorticosterone stimulates the collecting tubules in the kidney to continue to excrete potassium in much the same way that aldosterone does. Deoxycorticosterone has about 1/20 of the sodium retaining power of aldosterone and about 1/5 the potassium excreting power of aldosterone (Wikipedia). Deoxycorticosterone can be found throughout all human tissues and has been detected in amniotic fluid and blood. When present in sufficiently high levels, deoxycorticosterone can act as a hypertensive agent and a metabotoxin. A hypertensive agent increases blood pressure and causes the production of more urine. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Chronically high levels of deoxycorticosterone are associated with congenital adrenal hyperplasia (CAH) and with adrenal tumors producing deoxycorticosterone (PMID: 20671982). High levels of this mineralocorticoid are associated with resistant hypertension, which can result in polyuria, polydipsia, increased blood volume, edema, and cardiac enlargement. Deoxycorticosterone can be used to treat adrenal insufficiency. In particular, desoxycorticosterone acetate (DOCA) is used as replacement therapy in Addison's disease.

4-Pyridoxic acid is the catabolic product of vitamin B6 (also known as pyridoxine, pyridoxal and pyradoxamine) which is excreted in the urine. Urinary levels of 4-pyridoxic acid are lower in females than in males and will be reduced in persons with riboflavin deficiency. 4-Pyridoxic acid is formed by the action of aldehyde oxidase I (an endogenous enzyme) and by microbial enzymes (pyridoxal 4-dehydrogenase), an NAD-dependent aldehyde dehydrogenase. 4-pyridoxic acid can be further broken down by the gut microflora via 4-pyridoxic acid dehydrogenase. This enzyme catalyzes the four electron oxidation of 4-pyridoxic acid to 3-hydroxy-2-methylpyridine-4,5-dicarboxylate, using nicotinamide adenine dinucleotide as a cofactor.

alpha-Ketoisovaleric acid is an abnormal metabolite that arises from the incomplete breakdown of branched-chain amino acids. alpha-Ketoisovaleric acid is a neurotoxin, an acidogen, and a metabotoxin. A neurotoxin causes damage to nerve cells and nerve tissues. An acidogen is an acidic compound that induces acidosis, which has multiple adverse effects on many organ systems. A metabotoxin is an endogenously produced metabolite that causes adverse health effects at chronically high levels. Chronically high levels of alpha-ketoisovaleric acid are associated with maple syrup urine disease. MSUD is a metabolic disorder caused by a deficiency of the branched-chain alpha-keto acid dehydrogenase complex (BCKDC), leading to a buildup of the branched-chain amino acids (leucine, isoleucine, and valine) and their toxic by-products (ketoacids) in the blood and urine. The symptoms of MSUD often show in infancy and lead to severe brain damage if untreated. MSUD may also present later depending on the severity of the disease. If left untreated in older individuals, during times of metabolic crisis, symptoms of the condition include uncharacteristically inappropriate, extreme, or erratic behaviour and moods, hallucinations, anorexia, weight loss, anemia, diarrhea, vomiting, dehydration, lethargy, oscillating hypertonia and hypotonia, ataxia, seizures, hypoglycemia, ketoacidosis, opisthotonus, pancreatitis, rapid neurological decline, and coma. In maple syrup urine disease, the brain concentration of branched-chain ketoacids can increase 10- to 20-fold. This leads to a depletion of glutamate and a consequent reduction in the concentration of brain glutamine, aspartate, alanine, and other amino acids. The result is a compromise of energy metabolism because of a failure of the malate-aspartate shuttle and a diminished rate of protein synthesis (PMID: 15930465). alpha-Ketoisovaleric acid is a keto-acid, which is a subclass of organic acids. Abnormally high levels of organic acids in the blood (organic acidemia), urine (organic aciduria), the brain, and other tissues lead to general metabolic acidosis. Acidosis typically occurs when arterial pH falls below 7.35. In infants with acidosis, the initial symptoms include poor feeding, vomiting, loss of appetite, weak muscle tone (hypotonia), and lack of energy (lethargy). These can progress to heart, liver, and kidney abnormalities, seizures, coma, and possibly death. These are also the characteristic symptoms of untreated MSUD. Many affected children with organic acidemias experience intellectual disability or delayed development.

p-Hydroxyphenylacetic acid is an oxidative deaminated metabolite of p-tyramine. Also a metabolite of tyrosine via enteric bacteria. The bacterial origin of this compound was confirmed by the finding that this compound in urine decreased significantly after the use of the antibiotic neomycin.

Iodotyrosine is an iodated derivative of L-tyrosine. This is an early precursor to L-thyroxine, one of the primary thyroid hormones. In the thyroid gland, iodide is trapped, transported, and concentrated in the follicular lumen for thyroid hormone synthesis. Before trapped iodide can react with tyrosine residues, it must be oxidized by thyroid peroxidase. Iodotyrosine is made from tyrosine via thyroid peroxidase and then further iodinated by this enzyme to make the di-iodo and tri-iodo variants. Two molecules of di-iodotyrosine combine to form T4, and one molecule of mono-iodotyrosine combines with one molecule of di-iodotyrosine to form T3.

The O-methylated derivative of dopamine. Dopamine is methylated by catechol-O-methyltransferase (COMT) to make 3-Methoxytyramine. This compound can be broken down to homovanillic acid by monoamine oxidase and aldehyde dehydrogenase. Elevated concentrations of this compound are indicated for a variety of brain and carcinoid tumors as well as certain mental disorders.

(S)-3-Hydroxyisobutyric (3-HIBA) acid is an organic acid. 3-HIBA is an intermediate in L-valine metabolism. 3-HIBA plays an important role in the diagnosis of the very rare inherited metabolic diseases 3-hydroxyisobutyric aciduria (OMIM 236795) and methylmalonic semialdehyde dehydrogenase deficiency (OMIM 603178). Patients with 3-hydroxyisobutyric aciduria excrete a significant amount of 3-HIBA not only during the acute stage but also when stable. 3-hydroxyisobutyric aciduria is caused by a 3-hydroxyisobutyryl-CoA dehydrogenase deficiency (PMID: 18329219). The severity of this disease varies from case to case. Most patients exhibit dysmorphic features, such as a small triangular face, a long philtrum, low set ears and micrognathia (PMID: 113770040, 10686279). Lactic acidemia is also found in the affected patients, indicating that mitochondrial dysfunction is involved. 3-hydroxyisobutyrate appears to specifically inhibit the function of the respiratory chain complex I-III and mitochondrial creatine kinase (PMID: 18329219).

Ureidopropionic acid is an intermediate in the metabolism of uracil. More specifically it is a breakdown product of dihydrouracil and is produced by the enzyme dihydropyrimidase. It is further decomposed to beta-alanine via the enzyme beta-ureidopropionase. Ureidopropionic acid is essentially a urea derivative of beta-alanine. High levels of Ureidopropionic acid are found in individuals with beta-ureidopropionase (UP) deficiency [PMID: 11675655]. Enzyme deficiencies in pyrimidine metabolism are associated with a risk for severe toxicity against the antineoplastic agent 5-fluorouracil.

Tetrahydrobiopterin or BH4 is a cofactor in the synthesis of nitric oxide. In fact it is used by all three human nitric-oxide synthases (NOS) eNOS, nNOS, and iNOS as well as the enzyme glyceryl-ether monooxygenase. It is also essential in the conversion of phenylalanine to tyrosine by the enzyme phenylalanine-4-hydroxylase; the conversion of tyrosine to L-dopa by the enzyme tyrosine hydroxylase; and conversion of tryptophan to 5-hydroxytryptophan via tryptophan hydroxylase. Specifically, tetrahydrobiopterin is a cofactor for tryptophan 5-hydroxylase 1, tyrosine 3-monooxygenase, and phenylalanine hydroxylase all of which are essential for the formation of the neurotransmitters dopamine, noradrenaline and adrenaline. Tetrahydrobiopterin has been proposed to be involved in promotion of neurotransmitter release in the brain and the regulation of human melanogenesis. A defect in BH4 production and/or a defect in the enzyme dihydropteridine reductase (DHPR) causes phenylketonuria type IV, as well as dopa-responsive dystonias. BH4 is also implicated in Parkinson's disease, Alzheimer's disease and depression. Tetrahydrobiopterin is present in probably every cell or tissue of higher animals. On the other hand, most bacteria, fungi and plants do not synthesize tetrahydrobiopterin. -- Wikipedia.

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 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 signaling. Posttranscriptional events related to ribosomal activity and protein folding may further contribute to 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 signaling and chromatin structure are consistent with the notion that biotin has a unique significance in cell biology. (PMID: 15992684, 16011464).

Androsterone is an inactive breakdown metabolite of testosterone, the product of a reaction mediated by the enzyme oxidative 17beta-hydroxysteroid dehydrogenase (EC 1.1.1.51, 17beta-HSD). Androsterone can also be metabolized from other adrenal androgens such as dehydroepiandrosterone, dihydrotestosterone, or androstenedione, and is considered an inactive end product. However, it can be a physiological effector in its own right. Androsterone might be converted back to dihydrotestosterone. Humans (and other primates) are unique among mammals in having high levels of circulating androsterone glucuronide, a process that is the major role of uridine-diphospho-glucuronosyltransferase enzymes (EC 2.4.1.17, UGT) for glucuronidation of steroid metabolism in humans. Conjugation of androsterone is a pathway found in all vertebrates and it is widely recognized that the liver is a major site of glucuronidation. However, it is now clear that extrahepatic tissues are also involved in the conjugation of compounds to which these tissues are exposed. High levels of androsterone glucuronide found in the human prostate, breast cyst fluid, and ovary follicular fluid suggest that glucuronidation of 5alpha-reduced C19 steroids occurs in these tissues as well. In doping control, the ratio of androsterone/etiocholanolone provides valuable information that allows the assignment of a urine specimen to a particular person or the identification of urine samples with identical steroid profiles; this is particularly important to detect attempts of urine manipulation including urine alteration and substitution (PMID: 9188497, 17017935, 14643063, 12943709, 9699884, 17260133).