Methionine synthase also known as MS, MeSe, MTR is responsible for the regeneration of methionine from homocysteine. 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.
Methyltransferases are a large group of enzymes that all methylate their substrates but can be split into several subclasses based on their structural features. The most common class of methyltransferases is class I, all of which contain a Rossmann fold for binding S-Adenosyl methionine (SAM). Class II methyltransferases contain a SET domain, which are exemplified by SET domain histone methyltransferases, and class III methyltransferases, which are membrane associated. Methyltransferases can also be grouped as different types utilizing different substrates in methyl transfer reactions. These types include protein methyltransferases, DNA/RNA methyltransferases, natural product methyltransferases, and non-SAM dependent methyltransferases. SAM is the classical methyl donor for methyltransferases, however, examples of other methyl donors are seen in nature. The general mechanism for methyl transfer is a SN2-like nucleophilic attack where the methionine sulfur serves as the leaving group and the methyl group attached to it acts as the electrophile that transfers the methyl group to the enzyme substrate. SAM is converted to S-Adenosyl homocysteine (SAH) during this process. The breaking of the SAM-methyl bond and the formation of the substrate-methyl bond happen nearly simultaneously. These enzymatic reactions are found in many pathways and are implicated in genetic diseases, cancer, and metabolic diseases. Another type of methyl transfer is the radical S-Adenosyl methionine (SAM) which is the methylation of unactivated carbon atoms in primary metabolites, proteins, lipids, and RNA.
Histone-arginine N-methyltransferase is an enzyme with systematic name S-adenosyl-L-methionine:histone-arginine Nomega-methyltransferase. This enzyme catalyses the following chemical reaction
N-Acetylserotonin O-methyltransferase, also known as ASMT, is an enzyme which catalyzes the final reaction in melatonin biosynthesis: converting Normelatonin to melatonin. This reaction is embedded in the more general tryptophan metabolism pathway. The enzyme also catalyzes a second reaction in tryptophan metabolism: the conversion of 5-hydroxy-indoleacetate to 5-methoxy-indoleacetate. The other enzyme which catalyzes this reaction is n-acetylserotonin-o-methyltransferase-like-protein.
Histamine N-methyltransferase is an enzyme involved in the metabolism of histamine. It is one of two enzymes involved in the metabolism of histamine in mammals, the other being diamine oxidase (DAO). HNMT catalyzes the methylation of histamine in the presence of S-adenosylmethionine (SAM-e) forming N-methylhistamine. The HNMT enzyme is present in most body tissues but is not present in serum. Histamine N-methyltransferase is encoded by a single gene, HNMT, which in humans has been mapped to chromosome 2.
Guanidinoacetate N-methyltransferase is an enzyme that catalyzes the chemical reaction and is encoded by gene GAMT located on chromosome 19p13.3.
In enzymology, a magnesium protoporphyrin IX methyltransferase is an enzyme that catalyzes the chemical reaction
In enzymology, a mRNA (guanine-N7-)-methyltransferase also known as mRNA cap guanine-N7 methyltransferase is an enzyme that catalyzes the chemical reaction
In enzymology, a nicotinamide N-methyltransferase (NNMT) is an enzyme that catalyzes the chemical reaction
Carnosine synthase is an enzyme that catalyzes the chemical reaction
Protein arginine N-methyltransferase 6 is an enzyme that in humans is encoded by the PRMT6 gene.
Cobalamin biosynthesis is the process by which bacteria and archea make cobalamin, vitamin B12. Many steps are involved in converting aminolevulinic acid via uroporphyrinogen III and adenosylcobyric acid to the final forms in which it is used by enzymes in both the producing organisms and other species, including humans who acquire it through their diet.
Radical SAM is a designation for a superfamily of enzymes that use a [4Fe-4S]+ cluster to reductively cleave S-adenosyl-L-methionine (SAM) to generate a radical, usually a 5′-deoxyadenosyl radical (5'-dAdo), as a critical intermediate. These enzymes utilize this radical intermediate to perform diverse transformations, often to functionalize unactivated C-H bonds. Radical SAM enzymes are involved in cofactor biosynthesis, enzyme activation, peptide modification, post-transcriptional and post-translational modifications, metalloprotein cluster formation, tRNA modification, lipid metabolism, biosynthesis of antibiotics and natural products etc. The vast majority of known radical SAM enzymes belong to the radical SAM superfamily, and have a cysteine-rich motif that matches or resembles CxxxCxxC. rSAMs comprise the largest superfamily of metal-containing enzymes.
Uroporphyrinogen-III C-methyltransferase, uroporphyrinogen methyltransferase, uroporphyrinogen-III methyltransferase, adenosylmethionine-uroporphyrinogen III methyltransferase, S-adenosyl-L-methionine-dependent uroporphyrinogen III methylase, uroporphyrinogen-III methylase, SirA, CysG, CobA, uroporphyrin-III C-methyltransferase, S-adenosyl-L-methionine:uroporphyrin-III C-methyltransferase) is an enzyme with systematic name S-adenosyl-L-methionine:uroporphyrinogen-III C-methyltransferase. This enzyme catalyses the following chemical reaction
Sarcosine/dimethylglycine N-methyltransferase is an enzyme with systematic name S-adenosyl-L-methionine:sarcosine(or N,N-dimethylglycine) N-methyltransferase . This enzyme catalyses the following chemical reaction
Demethylmenaquinone methyltransferase is an enzyme with systematic name S-adenosyl-L-methionine:demethylmenaquinone methyltransferase. This enzyme catalyses the following chemical reaction
Demethylrebeccamycin-D-glucose O-methyltransferase is an enzyme with systematic name S-adenosyl-L-methionine:demethylrebeccamycin-D-glucose O-methyltransferase. This enzyme catalyses the following chemical reaction
tRNA (cytidine56-2'-O)-methyltransferase is an enzyme with systematic name S-adenosyl-L-methionine:tRNA (cytidine56-2'-O)-methyltransferase. This enzyme catalyses the following chemical reaction
tRNA (guanine37-N1)-methyltransferase (EC 2.1.1.228, TrmD, tRNA (m1G37) methyltransferase, transfer RNA (m1G37) methyltransferase, Trm5p, TRMT5, tRNA-(N1G37) methyltransferase, MJ0883 (gene)) is an enzyme with systematic name S-adenosyl-L-methionine:tRNA (guanine37-N1)-methyltransferase. This enzyme catalyses the following chemical reaction
[Fructose-bisphosphate aldolase]-lysine N-methyltransferase (EC 2.1.1.259) is an enzyme that catalyses the following chemical reaction
