Hydroxymethyltransferase

L-serine glycine + formaldehyde serine hydroxymethyltransferase E. coli 201... 

The conversion of a-ketoisovalerate (32) to ketopantoate (21) is cataly2ed by ketopantonate hydroxymethyltransferase and a cofactor tetrahydrofolate (65). Further reduction of ketopantoate (21) to (R)-pantoate (22) is cataly2ed by ketopantoic acid reductase (66). 

The metabolism of P-hydroxy-a-amino adds involves pyridoxal phosphate-dependent enzymes, dassified as serine hydroxymethyltransferase (SHMT) (EC 2.1.2.1) or threonine aldolases (ThrA L-threonine selective = EC 4.1.2.5, L-aHo-threonine selective = EC 4.1.2.6). Both enzymes catalyze reversible aldol-type deavage reactions yielding glycine (120) and an aldehyde (Eigure 10.45) [192]. 

Figure28-7. The serine hydroxymethyltransferase reaction. The reaction is freely reversible. (H4 folate, tetrahyd rofolate.)...

Serine. Following conversion to glycine, catalyzed by serine hydroxymethyltransferase (Figure 30—5), serine catabolism merges with that of glycine (Figure 30-6). 

Figure 30-5. Interconversion of serine and glycine catalyzed by serine hydroxymethyltransferase. (H4 folate, tetrahydrofolate.)...

Daly, E. C. Aprison, M. H. (1974). Distribution of serine hydroxymethyltransferase and glycine transaminase in several areas of the central nervous system of the rat. J. Neurochem. 22, 877-85. 

FIGURE 40-3 Glycine cleavage system and some related reactions. Glycine and serine are readily interchangeable. Enzymes (1) Glycine cleavage system (2) and (4) Serine hydroxymethyltransferase (3) N5 10-methylenetetrahydrolate reductase. N5 I0-CH2-FH4, N5>10-methylenetetrahydrolate FH4, tetrahydrofolic acid. 

A. Artigues, H. Farrant, V. Schirch, Cytosolic Serine Hydroxymethyltransferase. Deamidation of Asparaginyl Residues and Degradation in Xenopus laevis Oocytes , J. Biol. Chem. 1993, 268, 13784-13790. 

M. L. Di Salvo, S. Delle Fratte, B. Maras, F. Bossa, H. T. Wright, V. Schirch, Deamidation of Asparagine Residues in a Recombinant Serine-Hydroxymethyltransferase , Arch. Biochem. Biophys. 1999, 372, 271-279. 

This pyridoxal-phosphate-dependent enzyme [EC 2.1.2.1], which has a recommended EC name of glycine hydroxymethyltransferase, catalyzes the reversible reaction of 5,10-methylenetetrahydrofolate with glycine and water to produce tetrahydrofolate and L-serine. The enzyme will also catalyze the reaction of glycine with acetaldehyde to form L-threonine as well as with 4-tri-methylammoniobutanal to form 3-hydioxy-N, N, N -trimethyl-L-lysine. 

SERINE DEHYDRATASE SERINE DEHYDROGENASE SERINE HYDROXYMETHYLTRANSFERASE SERINE PALMITOYLTRANSFERASE Serine deaminase... 

SERINE DEHYDRATASE SERINE DEHYDRATASE SERINE DEHYDROGENASE Serine esterase inhibitor, irreversible, PHENYLMETHYLSULFONYL FLUORIDE SERINE HYDROXYMETHYLTRANSFERASE SERINE PALMITOYLTRANSFERASE Serine protease inhibitor, irreversible, PHENYLMETHYLSULFONYL FLUORIDE Serine proteinase inhibitor,... 

Saraiva LM, Vicente JB, Teixeira M (2004) The role of the flavodiiron proteins in microbial nitric oxide detoxification. Adv Microb Physiol 49 77-129 Schirch V, Szebenyi DME (2005) Serine hydroxymethyltransferase revisited. Curr Opin Chem Biol 9 482-487... 

In the laboratory, serine hydroxymethyltransferase will catalyze the conversion of threonine to glycine and acetaldehyde in one step, but this is not a significant pathway for threonine degradation in mammals. 

The enzyme serine hydroxymethyltransferase requires pyridoxal phosphate as cofactor. Propose a mechanism for the reaction catalyzed by this enzyme, in the direction of serine degradation (glycine production). (Hint See Figs 18-19 and 18-20b.)... 

RGURE 22-44 Conversion of dUMP to dTMP by thymidylate synthase and dihydrofolate reductase. Serine hydroxymethyltransferase is required for regeneration of the /V5,/V10-methylene form of tetrahy-... 

Side chain cleavage (Group c). In a third type of reaction the side chain of the Schiff base of Fig. 14-5 undergoes aldol cleavage. Conversely, a side chain can be added by (3 condensation. The best known enzyme of this group is serine hydroxymethyltransferase, which converts serine to glycine and formaldehyde.211-21313 The latter is not released in a free form but is transferred by the same enzyme specifically to tetrahydrofolic acid (Eq. 14-30), with which it forms a cyclic adduct. 

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