Methionine active

Methylmercaptopropionaldehyde is also used to make the methionine hydroxy analog CH2SCH2CH2CH(OH)COOH [583-91 -5] which is used commercially as an effective source of methionine activity (71). AH commercial syntheses of methionine and methionine hydroxy analog are based on the use of acrolein as a raw material. More than 170,000 tons of this amino acid are produced yearly (30) (see Amino acids). One method for the preparation of methionine from acrolein via 3-methyhnercaptopropionaldehyde is as follows. 

Spermidine 4 was biosynthesized from putrescine 2 (NC4N), obtained by ornithine 1, and adenosyl-L-methionine (activated C3 unit). S -Adenosyl-L-methioninamine (decarboxylated 5-adenosyl-L-methionine) donates an aminopropyl group to putrescine 2 to form spermidine 4 in a reaction catalyzed by spermidine synthase. Homospermidine 3 is formed from two moles of putrescine 2 in an NAD" -dependent reaction catalyzed by HSS. Moreover, HSS catalyzes the NADI-dependent transfer of an aminobutyl group of spermidine 4 to putrescine 2 to form homospermidine 3. 

S-Adenosyl-L-methionine, S-(S -ikaxyadenosme-5 )-methionme, active methionine, active methyl, SAM a reactive sulfonium compound (Fig.) (M, of free cation 398.4), and the most important methylating agent in cellular metabolism (see liansmethyla-tion). 

S-Adenosyl-L-methionine ( activated methionine ) is a sulfonium compound, which possesses the reactive —group. 

Norepinephrine is methylated in the presence of a specific enzyme (S-adenosylmethionine transferase) and a cofactor (S-adenosylmethionine) to form epinephrine. This reaction is analogous to the methyla-tion of guanidinoacetic acid, which occurs in liver. Two distinct enzyme reactions are involved methionine is converted to S-adenosylmethionine in the presence of a methionine-activating enzyme and ATP, in which reaction all the phosphates of ATP are lost, the terminal phosphorus of ATP is liberated as inorganic phosphate and the two internal phosphoryl groups yield pyrophosphate and (2) norepinephrine is then methylated in the presence of a specific enzyme S-adenosylmethionine transferase to form epinephrine. 

In the last analysis, the labile methyl group always passes to the acceptor from methionine. This is an operation requiring ATP. In fact, the true donor is methionine activated by ATP, or S-adenosyl-methionine. 

Because of its role in activating methionine for transmethylation, this enzyme was initially called the methionine-activating enzyme. With the later discovery of enzymes which activate the carboxyl group of methionine and other amino acids for protein synthesis, this term became somewhat confusing. In this chapter, the trivial name methionine adenosyltransferase or adenosyhransferase, will be used in accord with the recommendation of the Commission on Enzymes (Enzyme Nomenclature, American Elsevier, New York, 1965). The enzyme has also been called S-adenosylmethionine synthetase. 

Now let us consider the simple phenols. In the case we were studying /7-hydroxybenzoic acid is decarboxylated to hydroquinone and can be glucosylated to arbutin by means of UDPG. For the formation of the methyl ethers of hydroquinone and arbutin, S -adenosyl methionine, active methionine, serves as the methyl group donor. 

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