Methionine isolation

Creatine was first isolated in 1835 by Chevreul 20 years later Dessaignes showed it to contain a methyl group. Choline was obtained from lecithin in bile by Strecker in 1849 and methionine isolated by Mueller in 1922. That methionine contained a methyl group linked to sulfur was demonstrated by Barger and Coyne in 1928. 

Activity was also detected in S-adenosyl-L-methionine isolated from the plants. 

The significance of industrial acrolein production may be clearer if one considers the two major uses of acrolein—direct oxidation to acryUc acid and reaction to produce methionine via 3-methyhnercaptopropionaldehyde. In acryUc acid production, acrolein is not isolated from the intermediate production stream. The 1990 acryUc acid production demand in the United States alone accounted for more than 450,000 t/yr (28), with worldwide capacity approaching 1,470,000 t/yr (29). Approximately 0.75 kg of acrolein is required to produce one kilogram of acryUc acid. The methionine production process involves the reaction of acrolein with methyl mercaptan. Worldwide methionine production was estimated at about 170,000 t/yr in 1990 (30). (See Acrylic ACID AND DERIVATIVES AmINO ACIDS, SURVEY.)... 

The ansa-chain of the ansamycins streptovaricins (4), rifamycins (263), geldanamycin (4), and herbimycin (32) has been shown to be polyketide in origin, being made up of propionate and acetate units with the 0-methyl groups coming from methionine. The remaining aromatic C N portion of the ansamacroHdes is derived from 3-amino-5-hydroxybenzoic acid (264—266) which is formed via shikimate precursors. Based on the precursors of the rifamycins and streptovaricins isolated from mutant bacteria strains, a detailed scheme for the biosynthesis of most of the ansamacroHdes has been proposed (95,263). 

Sulfoxides occur widely in small concentrations in plant and animal tissues, eg, aHyl vinyl sulfoxide [81898-53-5] in garlic oil and 2,2 -sulfinylbisethanol [3085-45-8] as fatty esters in the adrenal cortex (1,2). Homologous methyl sulfinyl alkyl isothiocyanates, which are represented by the formula CH3SO(CH2) NCS, where n = 3 [37791-20-1], 4 [4478-93-7], 5 [646-23-1], 8 [75272-81-0], 9 [39036-83-4], or 10 [39036-84-5], have been isolated from a number of mustard oils in which they occur as glucosides (3). Two methylsulfinyl amino acids have also been reported methionine sulfoxide [454-41-1] from cockroaches and the sulfoxide of i -methylcysteine, 3-(methylsulfinyl)alaiiine [4740-94-7]. The latter is the dominant sulfur-containing amino acid in turnips and may account in part for their characteristic odor (4). 

Divalent sulfur compounds are achiral, but trivalent sulfur compounds called sulfonium stilts (R3S+) can be chiral. Like phosphines, sulfonium salts undergo relatively slow inversion, so chiral sulfonium salts are configurationally stable and can be isolated. The best known example is the coenzyme 5-adenosylmethionine, the so-called biological methyl donor, which is involved in many metabolic pathways as a source of CH3 groups. (The S" in the name S-adenosylmethionine stands for sulfur and means that the adeno-syl group is attached to the sulfur atom of methionine.) The molecule has S stereochemistry at sulfur ana is configurationally stable for several days at room temperature. Jts R enantiomer is also known but has no biological activity. 

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. 

As noted above, the presence of Met(O) in proteins would go undetected after acid hydrolysis and subsequent amino acid analysis. Thus, since this method of hydrolysis is most commonly used, it is impossible to ascertain from the literature the abundance of Met(O) residues normally present in proteins. However, a number of studies have reported the presence of Met(O) residues in various proteins using one of the appropriate procedures described above. It has been found that Met(O) residues comprise 30% of the total Met in proteins isolated from bovine glomerular basement membranes and anterior lens . Other investigators have reported that the levels of Met(O) in proteins of the trabecular meshwork of human eyes increased with the age of the donor . The amount of Met(O) detected ranged from 15% (10 years old) to 55% (79 years old) of the total methionine content found in the tissue samples. Other studies have shown that in certain species of clams the proteins of the hinge ligament contain only Met(0) residues and no Met . In addition, it has also been reported that as much as 18% of the Met residues in pea seed proteins is in the form of Met(O) . Lastly, Met(O) residues have been found in... 

Although single-electron-transfer (SET) processes would be expected to be important in reactions that use metals as reagents, this type of process has also been recognized in the reduction of carbonyl groups that involve 1,4-dihydronicotinamide derivatives . Recent work by Oae and coworkers" has shown that an SET process is operative in the reduction of dibenzothiophene S-oxide by l-benzyl-l,4-dihydronicotinamide when the reaction is catalyzed by metalloporphins. The reaction is outlined in equation (18), but the study gave results of much more mechanistic than synthetic value. This type of study is relevant to understanding biochemical mechanisms since it is known that methionine sulphoxide is reduced to methionine by NADPH when the reaction is catalyzed by an enzyme isolated from certain yeasts . 

Alpha-l-antiprotease (ai-AP) limits tissue damage arising from the actions of the leucocyte protease, elastase (Carrell and Travis, 1985), and there is much evidence available for the oxidative inactivation of this protein by oxygen-derived free-radical species and hypochlorous acid/hypochlorite anion (HOCl/OCP). The mechanism of this inactivation appears to involve the oxidation of a critical methionine residue (Met-358) to its corresponding sulphoxide and methionine sulphoxide has been detected in ai-AP samples isolated from the lungs of cigarette smokers (Carp et al., 1982) and rheumatoid synovial fluids (Wong and Travis, 1980). 

Delta receptors are relatively selective for two related penta-peptides, methionine enkephalin and leucine enkephalin (met- and leu-enkephalin), which were isolated from porcine brain (Hughes 1975). Both met- and leu-enkephalin inhibit electrically induced contractions of guinea pig ileum, an effect that mimics those effects seen with opioid drugs, and is naloxone reversible. The enkephalins are processed posttranslational ly from proenkephalin, and secreted from central and peripheral neurons and endocrine cells in the adrenal medulla. 

Aminopeptidase A is another brush border membrane enzyme which has been the subject of various studies [79,81,83-86], It has been found in the intestinal brush border membrane of humans, rabbits, rats, and pigs and is active against peptides with acidic amino acids at the amino terminus. Its activity against dipeptides is more limited. Shoaf et al., isolated three rat brush border aminopeptidases with distinct but somewhat overlapping substrate specificities. These enzymes had preference for dipeptides containing methionine, arginine, or aspartic acid and glycine. The optimal pH for activity of aminopeptidase was reported to be 7-8. 

Isolated polynucleotide clusters from Rhodococcus opacus which encode four polypeptides possessing the activities of a NHase (a and /3 subunits), an auxiliary protein P15K that activates the NHase, and a cobalt transporter protein were expressed in Escherichia coli DSM 14459 cells [34]. Methionine nitrile was added continuously to a suspension of the transformant cells (5.6% w/v of wet cells) in phosphate buffer (50 mM, pH 7.5) at 20 °C, at a rate where the nitrile concentration did not exceed 15 g L 1 while maintaining the pH constant at 7.5. After 320 min, the nitrile was completely converted into amide, corresponding to a final product concentration of 176 gL1.4-Methylthio-a-hydroxybutyramide is readily hydrolyzed with calcium hydroxide, where the calcium salt of 4-methylthio-a-hydroxybutyric acid (MHA) can be directly used as a nutritional supplement in animal feed as an alternative to methionine or MHA. 

Hundreds of different natural amino acids have been found and isolated. In some cases, they are quite complex and have a variety of functions. The preparation and isolation of amino acids occurs either from biological material or via chemical synthesis. Several amino acids, such as glutamic acid and methionine, are now prepared on a scale of 100,000 tons per year. 

One day prior to the isolation of polysomes, approximately 5 million HeLa cells are plated into 10-cm dishes. The following day, the media is replaced with fresh DMEM and compound is added to a concentration previously determined to inhibit translation in vivo by 35S-methionine metabolic labeling (see previously). 

In an initial series of experiments, [Me-14C] methionine and [8-14C]adenine were injected into D. verrucosa hepatopancreas. After HPLC isolation, xylosyl-MTA was found consistently labelled in particular, in the experiment with labelled methionine 28.0% of the recovered radioactivity was found associated with xylosyl-MTA, while 12.1% was recovered in the adenosylmethionine... 

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