Methionine chemical structure

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. 

Dissection of the chemical structure of jamaicamides A-C led to the speculation that these metabolites derive from a mixture of polyketides (nine acetate units), amino acids (t-Ala and p-Ala), and the S-methyl group of methionine. To map out the biosynthetic subunits of these molecules, isotopically labeled precursors were supplied to I. majuscula JHB, and the labeling patterns discerned by NMR spectroscopy (Figure 6.12). From these experiments, insights were gained into the biochemical transformations that produce the jamaicamides, especially the mechanism of formation of the vinyl chloride group [157]. 

Figure 1 P. aeruginosa QS system. Its mechanism, (a) Biosynthesis of acyl-homoserine lactone (AHL). Abbreviations SAM, 5-adenosyl methionine ACP, acyl carrier protein, (b) General chemical structure of AHL molecules, generally called autoinducer-1 (AI-1). (c) Chemical structure of V. fischeri AI-1. (d) Chemical structure of P. aeruginosa 3-oxo-C y-HSL and (e) C4-HSL. (f) Pseuodomonas quinolone signal, PQS.

Figure 17.1 The chemical structures of L-methionine, and monofluoro- (MFM), difluoro-(DFM) and trifluoromethionine (TFM).

We have shown in the last topic that a triplet code with four letters (DNA/RNA bases) to choose from is mathematically sufficient to encode 20 amino acids, but is it structurally sufficient What is there about a set of three nucleotide bases that enables it to recognise and specify the very different chemical structure of a single amino acid Likewise, how can very similar codons specify very different amino acids. How is it that AUG can specify methionine while, with only one base different in each case, AAG specifies lysine, GUG specifies valine, AUC specifies isoleucine The answer to this puzzle lies, as so often, in the properties of a remarkable set of enzyme proteins and a matching set of RNA molecules called transfer RNA (tRNA), which together provide, in effect, an adaptor kit. 

The thermal generation of flavor is a very essential process for the "taste" of many different foodstuffs, e.g. cocoa, coffee, bread, meat. The resulting aromas are formed through non-enzymatic reactions mainly with carbohydrates, lipids, amino acids (proteins), and vitamins under the influence of heat. Thiamin (vitamin B ) and the amino acids, cysteine and methionine, belong to those food constituents which act as flavor precursors in thermal reactions. The role of thiamin as a potent flavor precursor is related to its chemical structure which consists of a thiazole as well as a pyrimidine moiety. The thermal degradation of this heterocyclic constituent leads to very reactive intermediates which are able to react directly to highly odoriferous flavor compounds or with degradation products of amino acids or carbohydrates. 

Figure 4.7 Chemical structures of the amino acids L- //o-isoleucine (L-aiLe), D-leucine (D-Leu), L-norvaline (L-Nva), D-methionine (D-Met), L-2-aminobutyric acid (L-Abu) and D-norleucine (D-Nle).

We may divide the sulfur compounds into primary and conjugated, the primary compounds forming a part of more complex chemical structures in the latter. The major primary sulfur compounds that have an established role in the normal biochemical processes of the vertebrate range in variety from the simple inorganic compounds, sulfate, thiosulfate, and thiocyanate, to the amino acids, cysteine, cystine, methionine,... 

Methylthioadenosine (MTA) represents one of the main products of S-adenosylmethionine (Ado-Met) metabolism and is distributed ubiquitously in micromolar amounts in several prokaryotes and eukaryotes . Although the chemical structure of this thioether was elucidated in 1924, its biological role as product of methionine metabolism was demonstrated by Schlenk in 1952, even before the discovery of its precursor Ado-Met. ... 

FIGURE 3.5 Chemical structure of the essential amino adds, (a) Lysine, (b) Tryptophan, (c) Methionine, (d) Threonine, (e) Phenylalanine, (f) Leudne. (g) Isoleudne. (h) Valine, (i) Histidine. 

Of the twenty amino acids that are normally found in proteins, only two contain sulfur, cysteine and methionine. Cysteine has long been recognized as being easily oxidized and this oxidation is associated with the loss of biological activity of many proteins. In recent years, it has been shown that methionine also shares these characteristics. Methionine was first isolated by Mueller19 and was one of the last amino acids discovered. Its structure was later proven to be y-methylthio-a-aminobutyric acid by Barger and Coyne20 who named the amino acid methionine as a contraction for its chemical name. 

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