Serine hydroxymethyl transferase

Several strategies for the production of pure D- or L-amino acids rely on the use of enzymes. L-Serine (49) is synthesized by combining glycine (48) and formaldehyde in the presence of the enzyme serine hydroxymethyl transferase (66). 

Pyridoxamine phosphate serves as a coenzyme of transaminases, e.g., lysyl oxidase (collagen biosynthesis), serine hydroxymethyl transferase (Cl-metabolism), S-aminolevulinate synthase (porphyrin biosynthesis), glycogen phosphoiylase (mobilization of glycogen), aspartate aminotransferase (transamination), alanine aminotransferase (transamination), kynureninase (biosynthesis of niacin), glutamate decarboxylase (biosynthesis of GABA), tyrosine decarboxylase (biosynthesis of tyramine), serine dehydratase ((3-elimination), cystathionine 3-synthase (metabolism of methionine), and cystathionine y-lyase (y-elimination). 

Figure 10.45 Aldol reactions catalyzed in vivo by serine hydroxymethyl transferase and by threonine aldolases.

Serine hydroxymethyl transferase catalyzes the decarboxylation reaction of a-amino-a-methylmalonic acid to give (J )-a-aminopropionic acid with retention of configuration [1]. The reaction of methylmalonyl-CoA catalyzed by malonyl-coenzyme A decarboxylase also proceeds with perfect retention of configuration, but the notation of the absolute configuration is reversed in accordance with the CIP-priority rule [2]. Of course, water is a good proton source and, if it comes in contact with these reactants, the product of decarboxylation should be a one-to-one mixture of the two enantiomers. Thus, the stereoselectivity of the reaction indicates that the reaction environment is highly hydro-phobic, so that no free water molecule attacks the intermediate. Even if some water molecules are present in the active site of the enzyme, they are entirely under the control of the enzyme. If this type of reaction can be realized using synthetic substrates, a new method will be developed for the preparation of optically active carboxylic acids that have a chiral center at the a-position. 

The enzymatic reaction was performed at 30 °C for 2 hours in a volume of 1 ml of 250 mM phosphate buffer (pH 6.5) containing 50 mM of KOH, 32 U/ml of the enzyme, and [1- C]-substrate. The product was isolated as the methyl ester. When the (S)-enantiomer was employed as the substrate, C remained completely in the product, as confirmed by C NMR and HRMS. In addition, spin-spin coupling between and was observed in the product, and the frequency of the C-O bond-stretching vibration was down-shifted to 1690 cm" (cf. 1740 cm for C-O). On the contrary, reaction of the (R)-enantiomer resulted in the formation of (R)-monoacid containing C only within natural abundance. These results clearly indicate that the pro-R carboxyl group of malonic acid is ehminated to form (R)-phenylpropionate with inversion of configuration [28]. This is in sharp contrast to the known decarboxylation reaction by malonyl CoA decarboxylase [1] and serine hydroxymethyl transferase [2], which proceeds with retention of configuration. 

These three compounds exert many similar effects in nucleotide metabolism of chicks and rats [167]. They cause an increase of the liver RNA content and of the nucleotide content of the acid-soluble fraction in chicks [168], as well as an increase in rate of turnover of these polynucleotide structures [169,170]. Further experiments in chicks indicate that orotic acid, vitamin B12 and methionine exert a certain action on the activity of liver deoxyribonuclease, but have no effect on ribonuclease. Their effect is believed to be on the biosynthetic process rather than on catabolism [171]. Both orotic acid and vitamin Bu increase the levels of dihydrofolate reductase (EC 1.5.1.4), formyltetrahydrofolate synthetase and serine hydroxymethyl transferase in the chicken liver when added in diet. It is believed that orotic acid may act directly on the enzymes involved in the synthesis and interconversion of one-carbon folic acid derivatives [172]. The protein incorporation of serine, but not of leucine or methionine, is increased in the presence of either orotic acid or vitamin B12 [173]. In addition, these two compounds also exert a similar effect on the increased formate incorporation into the RNA of liver cell fractions in chicks [174—176]. It is therefore postulated that there may be a common role of orotic acid and vitamin Bj2 at the level of the transcription process in m-RNA biosynthesis [174—176]. 

Rebeille, F.,Neuburger,M., Douce, R. (1994). Interaction between glycine decarboxylase, serine hydroxymethyl-transferase and tetrahydrofolate polyglutamates in pea leaf mitochondria. Biochem. J., 302,223-228. 

Serine hydroxymethyl transferase SHMT MLKNVFHRF SSSWILSEKVL Mukherjee et al. (2006b)... 

Mukherjee M, Seivers SA, Brown MT, Johnson PJ (2006b) Identification and biochemical characterization of serine hydroxymethyl transferase in the hydrogenosome of Trichomonas vaginalis. Eukaryot Cell 5 2072-2078 Muller A, Rassow J, Grimm J, Machuy N, Meyer TF, Rudel T (2002) VDAC and the bacterial porin PorB of Neisseria gonorrhoeae share mitochondrial import pathways. EMBO J 21 1916-1929... 

Glycine is synthesized from serine by removal of a hydroxymethyl group, also by serine hydroxymethyl transferase (see Figure 20.6A). 

An intermediate analogous to that in figure 10.4/7 but generated from glycine and so lacking the /3 and y carbons, can react as a carbanion with an aldehyde to produce a /3-hydroxy-a-amino acid. These reactions are catalyzed by aldolases, such as threonine aldolase or serine hydroxymethyl transferase. 

Scheme 5.48. Enzymatic synthesis of 2-amino-3-hydroxy-l, 6-hexanedicarboxylic acids using serine hydroxymethyl transferases (SHMT). DEAD = diethyl azodicarboxylate.

Gly is synthesized in glycinergic nerve terminals from serine in a reaction catalyzed by serine hydroxymethyl transferase. Gly molecules are packaged into synaptic... 

Serine-hydroxymethyl transferase, methylenetetrahydrofolate reductase, and methyltetrahydrofolate-homocysteine methyltransferase, mechanism of biological methylation with 90CRV1275. 

The purified enzyme requires a methylene tetrahydrofolate cofactor [162]. The hydroxymethylation reaction proceeds with inversion [163] (Fig. 33) and probably occurs by a mechanism analogous to serine hydroxymethyl transferase [48]. 

Trivedi, V., Gupta, A., Jala, V.R., et al. (2002) Crystal structure of binary and ternary complexes of serine hydroxymethyl-transferase from Bacillus stearothermophilus Insights into the catalytic mechanism. /. Biol. Chem. 277, 17161-17169. 

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