Methionine is an essential amino acid in humans.
Homocysteine or Hcy: is a non-proteinogenic α-amino acid. It is a homologue of the amino acid cysteine, differing by an additional methylene bridge (-CH2-). It is biosynthesized from methionine by the removal of its terminal Cε methyl group. In the body, homocysteine can be recycled into methionine or converted into cysteine with the aid of vitamin B6, B9, and B12.
Homocystinuria (HCU) is an inherited disorder of the metabolism of the amino acid methionine due to a deficiency of cystathionine beta synthase or methionine synthase. It is an inherited autosomal recessive trait, which means a child needs to inherit a copy of the defective gene from both parents to be affected. Symptoms of homocystinuria can also be caused by a deficiency of vitamins B6, B12, or folate.
Methylenetetrahydrofolate reductase (MTHFR) is the rate-limiting enzyme in the methyl cycle, and it is encoded by the MTHFR gene. Methylenetetrahydrofolate reductase catalyzes the conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, a cosubstrate for homocysteine remethylation to methionine. Natural variation in this gene is common in otherwise healthy people. Although some variants have been reported to influence susceptibility to occlusive vascular disease, neural tube defects, Alzheimer's disease and other forms of dementia, colon cancer, and acute leukemia, findings from small early studies have not been reproduced. Some mutations in this gene are associated with methylenetetrahydrofolate reductase deficiency. Complex I deficiency with recessive spastic paraparesis has also been linked to MTHFR variants. In addition, the aberrant promoter hypermethylation of this gene is associated with male infertility and recurrent spontaneous abortion.
Trimethylglycine is an amino acid derivative with the formula (CH3)3N+CH2CO−2. A colorless, water-soluble solid, it occurs in plants. Trimethylglycine is a zwitterion: the molecule contains both a quaternary ammonium group and a carboxylate group. Trimethylglycine was the first betaine discovered; originally it was simply called betaine because it was discovered in sugar beets. Several other betaines are now known.
Methionine synthase (MS, MeSe, MTR) is primarily responsible for the regeneration of methionine from homocysteine in most individuals. In humans it is encoded by the MTR gene (5-methyltetrahydrofolate-homocysteine methyltransferase). Methionine synthase forms part of the S-adenosylmethionine (SAMe) biosynthesis and regeneration cycle, and is the enzyme responsible for linking the cycle to one-carbon metabolism via the folate cycle. There are two primary forms of this enzyme, the Vitamin B12 (cobalamin)-dependent (MetH) and independent (MetE) forms, although minimal core methionine synthases that do not fit cleanly into either category have also been described in some anaerobic bacteria. The two dominant forms of the enzymes appear to be evolutionary independent and rely on considerably different chemical mechanisms. Mammals and other higher eukaryotes express only the cobalamin-dependent form. In contrast, the distribution of the two forms in Archaeplastida (plants and algae) is more complex. Plants exclusively possess the cobalamin-independent form, while algae have either one of the two, depending on species. Many different microorganisms express both the cobalamin-dependent and cobalamin-independent forms.
Asymmetric dimethylarginine (ADMA) is a naturally occurring chemical found in blood plasma. It is a metabolic by-product of continual protein modification processes in the cytoplasm of all human cells. It is closely related to L-arginine, a conditionally essential amino acid. ADMA interferes with L-arginine in the production of nitric oxide (NO), a key chemical involved in normal endothelial function and, by extension, cardiovascular health.
Hyperhomocysteinemia is a medical condition characterized by an abnormally high level of total homocysteine in the blood, conventionally described as above 15 μmol/L.
S-Adenosyl-L-homocysteine (SAH) is the biosynthetic precursor to homocysteine. SAH is formed by the demethylation of S-adenosyl-L-methionine. Adenosylhomocysteinase converts SAH into homocysteine and adenosine.
LabCorp v. Metabolite, Inc., 548 U.S. 124 (2006), is the first case since Diamond v. Chakrabarty in which the U.S. Supreme Court indicated a renewed interest in examining the limits of patentable subject matter for advances in life sciences. Although the Court initially agreed to hear the case, it was later dismissed in 2006 with three Justices dissenting. The defendant's petition to the Supreme Court raised an issue not addressed in opinions from the lower courts: the claim at issue was directed to patent ineligible subject matter and therefore invalid.
Cystathionine-β-synthase, also known as CBS, is an enzyme (EC 4.2.1.22) that in humans is encoded by the CBS gene. It catalyzes the first step of the transsulfuration pathway, from homocysteine to cystathionine:
Hypermethioninemia is an excess of the amino acid methionine, in the blood. This condition can occur when methionine is not broken down properly in the body.
Cystathionine is an intermediate in the synthesis of cysteine from homocysteine. It is produced by the transsulfuration pathway and is converted into cysteine by cystathionine gamma-lyase (CTH).
Adenosylhomocysteinase (EC 3.13.2.1, S-adenosylhomocysteine synthase, S-adenosylhomocysteine hydrolase, adenosylhomocysteine hydrolase, S-adenosylhomocysteinase, SAHase, AdoHcyase) is an enzyme that catalyzes the nicotinamide adenine dinucleotide (NAD+) dependent, reversible hydrolysis of S-adenosylhomocysteine to homocysteine and adenosine.
Vitamin B12 deficiency, also known as cobalamin deficiency, is the medical condition in which the blood and tissue have a lower than normal level of vitamin B12. Symptoms can vary from none to severe. Mild deficiency may have few or absent symptoms. In moderate deficiency, feeling tired, headaches, soreness of the tongue, mouth ulcers, breathlessness, feeling faint, rapid heartbeat, low blood pressure, pallor, hair loss, decreased ability to think and severe joint pain and the beginning of neurological symptoms, including abnormal sensations such as pins and needles, numbness and tinnitus may occur. Severe deficiency may include symptoms of reduced heart function as well as more severe neurological symptoms, including changes in reflexes, poor muscle function, memory problems, blurred vision, irritability, ataxia, decreased smell and taste, decreased level of consciousness, depression, anxiety, guilt and psychosis. If left untreated, some of these changes can become permanent. Temporary infertility, reversible with treatment, may occur. A late finding type of anemia known as megaloblastic anemia is often but not always present. In exclusively breastfed infants of vegan mothers, undetected and untreated deficiency can lead to poor growth, poor development, and difficulties with movement.
In the field of enzymology, a betaine-homocysteine S-methyltransferase also known as betaine-homocysteine methyltransferase (BHMT) is a zinc metallo-enzyme that catalyzes the transfer of a methyl group from trimethylglycine and a hydrogen ion from homocysteine to produce dimethylglycine and methionine respectively:
In enzymology, a glutathione—homocystine transhydrogenase is an enzyme that catalyzes the chemical reaction
Oxycholesterol or 5,6-epoxycholesterol is a form of oxidized cholesterol implicated in atherosclerosis. It is commonly formed from the reaction of fats and oxygen during high temperature cooking such as frying.
Tricetin 3',4',5'-O-trimethyltransferase is an enzyme with systematic name S-adenosyl-L-methionine:tricetin 3',4',5'-O-trimethyltransferase. This enzyme catalyses the following chemical reaction
