S-adenosyl-L-methionine

Catechol O-methyltransferase (COMT) is a widespread enzyme that catalyzes the transfer of the methyl group of S-adenosyl-l-methionine (AdoMet) to one of the phenolic group of the catechol substrate (Fig. 1). High COMT activity is found in the liver, kidney and gut wall... 

S-adenosyl-L-methionine (AdoMet, SAM) is a cofactor and the most important donor of the methyl (CH3-) group for methyltransferases, including COMT. When the methyl-group has been transferred, the remaining demethylated compound is called S-adenosyl-L-homo-cysteine. 

De Luca, V. and Ibrahim, R. K. 1985a. Enzymatic synthesis of polymethylated flavonols of Chrys-osplenium americarmm. I. Partial purification and some properties of S-adenosyl-L-methionine flavonol 3-, 6-, 7-, and 4 -0-methyltransferases. Arch. Biochem. Biophys. 238 596-605. 

Esterification of the propionic acid side chain at C-13 (ring C) with a methyl group catalyzed by S-adenosyl-L-methionine-magnesium protoporphyrin 0-meth-yltransferase yields protoporphyrin IX monomethyl ester (MPE), which originates protochlorophyllide by a P-oxidation and cyclization of the methylated propionic side chain. This molecule contains a fifth isocyclic ring (ring E), the cyclopentanone ring that characterizes aU chlorophylls. 

Kauss, H., Swanson, A.L., and Hassid, W.Z. (1967) Biosynthesis of the methyl ester groups of pectin by transmethylation from S-adenosyl-L-methionine. Biochem.BiophysJies.Commun. 26 234-240. 

Mazzafera, P., Wingsle, G., Olsson, O., Sandberg, G., S-Adenosyl-L-methionine theobromine 1-N-methyltransferase, an enzyme catalyzing the synthesis of caffeine in coffee, Phytochemistry, 37(6), 1577, 1994. (CA122 259411n)... 

S-adenosyl-L-homocysteine S-adenosyl-L-methionine Su(var)3-9 (suppressor of variegation 3-9), E(z) (enhancer of zeste), and trithorax domain... 

JAMES, F., NOLTE, K.D., HANSON A.D., Purification and properties of S-adenosyl-L-methionine L-methionine S-methyltransferase from Wollastonia biflora leaves, J. Biol. Chem., 1995, 270,22343-22350. 

HOFFMAN, J.L., 1986. Chromatographic analysis of the chiral and covalent instability of S-adenosyl-L-methionine, Biochemistry, 1986, 25, 4444-4449. 

MORISHIGE, T TSUJITA, T YAMADA, Y SATO, F., Molecular characterization of the S-adenosyl-L-methionine 3 -hydroxy-A-methylcoclaurine 4 -0-methyltransferase involved in isoquinoline alkaloid biosynthesis in Coptis japonica, J. Biol. Chem., 2000, 275, 23398-23405. 

The methyltransferases represent a relatively large number of enzymes that utilize the cofactor, S-adenosyl-L-methionine, in which the methyl group is bound to a positively charged sulfur, to transfer a methyl group to an oxygen, sulfur, or nitrogen atom in an appropriate substrate as shown in Figure 7.9 (8). 

The possibility that many organic compounds could potentially be precursors of ethylene was raised, but direct evidence that in apple fruit tissue ethylene derives only from carbons of methionine was provided by Lieberman and was confirmed for other plant species. The pathway of ethylene biosynthesis has been well characterized during the last three decades. The major breakthrough came from the work of Yang and Hoffman, who established 5-adenosyl-L-methionine (SAM) as the precursor of ethylene in higher plants. The key enzyme in ethylene biosynthesis 1-aminocyclopropane-l-carboxylate synthase (S-adenosyl-L-methionine methylthioadenosine lyase, EC 4.4.1.14 ACS) catalyzes the conversion of SAM to 1-aminocyclopropane-l-carboxylic acid (ACC) and then ACC is converted to ethylene by 1-aminocyclopropane-l-carboxylate oxidase (ACO) (Scheme 1). 

Scheme 1 The ethylene biosynthetic pathway. The enzymes catalyzing each step are shown above the arrows. SAM S-adenosyl-L-methionine SAMS S-adenosyl-i-methionine synthetase ACC 1-aminocyclopropane-1-carboxylic acid ACS 1-aminocyclopropane-1-carboxylate synthase ACO 1-aminocyclopropane-1-carboxylate oxidase Ade adenine MTA methylthioadenosine. The atoms of SAM recycled to methionine through methionine cycle are marked in red and the atoms of methionine converted to ethylene are marked in bold. For details see text.

NADP Oxidized nicotinamide adenine SAM S-adenosyl L-methionine... 

In multicellular eukaryotes, DNA methylation is associated with transcriptional silencing [3]. In these organisms, DNA methylation has been observed exclusively on the C5 position of the cytosine ring and is frequently found in CpG-rich regions. This process is attributed to the action of DNA methyltransferases (DNMTs), which utilize the cofactor, S-adenosyl-L-methionine. Approximately half of all human genes have CpG islands in their promoter regions but these stretches of DNA are typically... 

Figure 13.1 (a) Trimethyllysine 4 and dimethylarginine 2 at histone H3 from X-ray structure [4]. (b) Chemical structure of the methylating agent S-adenosyl-L-methionine. 

This enzyme [EC 2.1.1.72] catalyzes the reaction of S-adenosyl-L-methionine with an adenine residue in DNA to produce S-adenosyl-L-homocysteine and a 6-methyl-aminopurine residue in DNA. 

Methyltransferases that utilize S-adenosyl-L-methionine as the methyl donor (and thus generating S-adenosyl-L-homocysteine) catalyze (a) A-methylation (e.g., norepinephrine methyltransferase, histamine methyltransferase, glycine methyltransferase, and DNA-(adenine-A ) methyltransferase), (b) O-methylation (e.g., acetylsero-tonin methyltransferase, catechol methyltransferase, and tRNA-(guanosine-0 ) methyltransferase), (c) S-methyl-ation (e.g., thiopurine methyltransferase and methionine S-methyltransferase), (d) C-methylation (eg., DNA-(cy-tosine-5) methyltransferase and indolepyruvate methyltransferase), and even (e) Co(II)-methylation during the course of the reaction catalyzed by methionine syn-thase. ... 

Crystal structures of methyltransferases suggest that S-adenosyl-L-methionine binds in an extended conforma-... 

Enzymatic O-methylation of flavonoids, which is catalyzed by O-methyltransferases (E.C. 2.1.1.6-) involves the transfer of the methyl group of an activated methyl donor, S -adenosyl-L-methionine, to the hydroxyl group of a flavonoid acceptor with the formation of the corresponding methylether and S -adenosyl-L-homocysteine. The latter product is, in... 

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