Methionine synthesis

Methyl isovalerate, azeotropic mixtures with butyl alcohols, 4 395t Methyl ketones, acetic anhydride used in synthesis, 1 148 Methyllithium, 14 249 15 147 Methylmagnesium chloride, 16 319 (R)-(—)-Methylmandelic acid chloride, chiral derivatizing reagent, 6 76t Methyl mercaptan production, 15 17 3-Methylmercaptopropionaldehyde (MMP), intermediate in methionine synthesis, 1 268, 269, 276... 

Dubnoff J, Borsook H (1948) Dimethylthetin and dimethyl-P-propiothetin in methionine synthesis. J Biol Chem 176 789-798... 

Nitrous oxide, which is also called laughing gas, is a weak anesthetic. It is usually used together with hypnotics, analgesics, and muscle relaxants. It is sometimes called an ideal anesthetic because of the absence of any kind of suppressive influence on respiration. However, according to the latest information, use of nitrous oxide for more than 2 h is counterproductive since it causes a severe reduction of methionine synthesis, which in turn can cause a severe decrease in the level of vitamin Bj2 with all its subsequent consequences. 

Danes, G., Kondrak, M., Banfalvi, Z. (2008). The effects of enhanced methionine synthesis on amino acid and anthocyanin content of potato tubers. BMC Plant Biol., 8, 65. 

Cysteine is formed in plants and in bacteria from sulfide and serine after the latter has been acetylated by transfer of an acetyl group from acetyl-CoA (Fig. 24-25, step f). This standard PLP-dependent (3 replacement (Chapter 14) is catalyzed by cysteine synthase (O-acetylserine sulfhydrase).446 447 A similar enzyme is used by some cells to introduce sulfide ion directly into homocysteine, via either O-succinyl homoserine or O-acetyl homoserine (Fig. 24-13). In E. coli cysteine can be converted to methionine, as outlined in Eq. lb-22 and as indicated on the right side of Fig. 24-13 by the green arrows. In animals the converse process, the conversion of methionine to cysteine (gray arrows in Fig. 24-13, also Fig. 24-16), is important. Animals are unable to incorporate sulfide directly into cysteine, and this amino acid must be either provided in the diet or formed from dietary methionine. The latter process is limited, and cysteine is an essential dietary constituent for infants. The formation of cysteine from methionine occurs via the same transsulfuration pathway as in methionine synthesis in autotrophic organisms. However, the latter use cystathionine y-synthase and P-lyase while cysteine synthesis in animals uses cystathionine P-synthase and y-lyase. 

Anilino-pyrimidines cyprodinil CBL >,CGS (L-methionine synthesis) 4,24 By-pass reactions mutation in cgs (S24P and I64V) , ABC transponeis ... 

Martinez-Chantar, M.L., Garcia-Trevijano, E.R., Latasa, M.U., Perez-Mato, I., Sanchez-del-Pino, M.M., Corrales, F.X, Avila, M.A., Mato, J.M. Importance of a deficiency in S-adenosyl-L-methionine synthesis in the pathogenesis of liver injury. Amer. J. Nutr. 2002 76 1177-1182... 

Support of purine and thymidylate synthesis also requires that the folate cofactor exist in the triglutamate form, or as longer derivatives. However, support of glycine and methionine synthesis by folate cofactors does not occur with the triglutamate, and requires longer-chain-length folates, i.e., folylpentaglutamates (Lowe ei al., 1993),... 

These cocnxymes derived from folic acid participate in many imponant reactions, including conversion ofhomocys-Icine to methionine, synthesis of glycine from serine, purine synthesis (C-2 and C-8). and hi.stidine metabolism. 

Once inside the cell, folates participate in a number of interconnected metabolic pathways involving (1) thymidine and purine biosynthesis necessary for DNA synthesis, (2) methionine synthesis via homocysteine remethylation, (3) methylation reactions involving S-adenosylmethionine (AdoMet), (4) serine and glycine interconversion, and (5) metabolism of histidine and formate (see Figure 8). Via these pathways. 

Fig. 12.7 Pathways of folate metabolism and use in microbial cells (upper) and mammalian cells (lower). Bacterial and protozoal cells must synthesize dihydrofolic acid (DHF) from p-aminobenzoic acid (PABA). DHF is converted to tetrahydrofolic acid (THF) by the enzyme dihydrofolate reductase (DHFR). THF supplies single carbon units for various pathways including DNA, RNA and methionine synthesis. Mammalian cells do not make DHF, it is supplied from the diet, conversion to THF occurs via a DHFR enzyme as in microbial cells.

Animals - Mammals require methionine (Met) in their diets (i.e.. Met is an essential amino acid) and Cys can be made from Met, as shown in Figure 2L7. Thus, Cys is nonessential as long as sufficient Met is present in the diet. Mammals make Met from homocysteine, as shown in the reaction here. Figure 2L8 shows the pathway from Met to Cys and reveals that it is quite similar to the reverse of the methionine synthesis pathway in bacteria shown in Figure 21.5. Plants and bacteria also use the pathway shown in Figure 2L8 so they can synthesize one from the other, depending on their immediate needs. Methionine can also be made by conversion of choline, as shown here. 

F. 47.7. The synthesis of creatine from arginine, glycine, and S-adenosyl methionine. Synthesis originates in the kidney and is completed in the hver. 

S ATP + 5-methylthioribose (<1> enzyme may be involved in an alternative pathway of methionine synthesis in plant tissues [1] <2> may be a primary enzyme involved in the recycling of the methylthio group of 5-methylthioribose back into methionine [2,3] <3> key step in recycling of methionine from 5 -methylthioadenosine a co-product of polyamine biosynthesis, expression of methylthioribose kinase may be under control of the methionine regulon [4]) (Reversibility [1-4, 6]) [1-4, 6, 7]... 

The tetrahydropterin-dithioiene iigand generated considerabie excitement and speculation. It was unique in biochemistry, and is unusual in chemistry. While dithiolenes were well-known ligands for molybdenum and other metals, this was the first time a dithioiene was proposed to play a role in biochemistry. On the other hand, tetrahydropterins were already known molecules in biochemical processes, such as the tetrahydrobiop-terin cofactor used by aromatic amino acid hydroxylases and tetrahydro-folate in Cl transfer in methionine synthesis (Figure 2.3). Certainly, this was the first time a pterin was found to be in combination with a dithioiene an where in chemistry. 

Cysteine inhibited sugar beet and radish threonine synthases. It was, therefore, proposed that O-phosphohomoserine would be diverted toward methionine synthesis as cysteine inhibited the enzyme (Madison and Thompson, 1976). Effective regulation could be achieved by the opposing effects of the methionine precursor, cysteine, and the methionine derivative, 5-adenosylmethionine. However, this can not be considered a universal regulatory pattern for plant threonine synthases since the barley enzyme was not inhibited by cysteine (Aarnes, 1978) and the effects of cysteine on the activity of the pea enzyme were questionable (Thoen et al., 1978b). 

Fig. 6. Control of methionine synthesis. Symbols are described in Fig. 2. Controls that have been observed consistently in plants are shown as thin continuous arrows, while those that have been observed in some plants, but not in others, are shown as dashed arrows.

In pea seedlings during germination there is a massive synthesis of homoserine, an intermediate in threonine and methionine synthesis (see Bryan, this volume. Chapter 11). There is little doubt that homoserine is derived from aspartate in pea chloroplasts (Lea et aL, 1979a) but whether this is the sole route of homoserine biosynthesis in pea seedlings is still in doubt (Mitchell and Bidwell, 1970 Bauer ef a/., 1977b). 

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