Serine: glyoxylate aminotransferase

Brock et al. (1970) resolved serine glyoxylate aminotransferase after incubating this enzyme at pH 5.6 in the presence of the substrate, L-serine. After subsequent precipitation with ammonium sulfate and dialysis against phosphate buffer, the enzyme had no activity. The activity was considerably restored by PLP and to a much lesser extent by pyridoxamine-P (Brock et al., 1970). 

Fig. 1. Main routes involved in the synthesis and interconversion of glycine and serine in plants. The various steps are numbered, and the necessary enzymes are as follows 1, glycolate oxidase, E.C. 1.1.3.1 2, aminotransferases, serine, E.C. 2.6.1.45, and glutamate, E.C. 2.6.1.4, glyoxylate aminotransferases 3, enzyme complex in mitochondria (see Fig. 2) 4, serine-glyoxylate aminotransferase, E.C. 2.6.1.45 5, glycerate dehydrogenase, E.C. 1.1.1.29 6, glycerate kinase E.C. 2.7.1.31 7, D-3-phosphoglycerate phosphatase, E.C. 3.1.3.38 8, d-3-phosphoglycerate dehydrogenase, E.C. 1.1.1.95 9, phosphoserine aminotransferase, E.C. 2.6.1.52 10, phosphoserine phosphatase, E.C. 3.1.3.3 11, serine hydroxymethyltransferase E.C. 2.1.2.1 12, nonenzymatic decarboxylation 13, formyl tetrahydrofolate synthetase, E.C. 6.3.4.3 14, isocitrate iyase, E.C. 4.1.3.1.

Somerville and Ogren (1980b) initially isolated a mutant of A. thaliana lacking peroxisomal serine glyoxylate aminotransferase. The mutant was detected by demonstrating that C02 accumulated in glycine and serine following photosynthesis in air. Similar mutant lines have also been detected in barley (Murray et al, 1987) and tobacco (Havir and McHale, 1988). 

Glycine (aminoacetic acid, aminoethanoic acid) is HjN. CHj.COOH, with = 2.4. It is transaminated by an ala-nine-glyoxylate aminotransferase. The glycine can then be incorporated into proteins and used for serine synthesis or simply be degraded. 

Aminopeptidase, cytosol Aminopeptidase, leucine Aminopropyltransferase, putrescine Aminotransferase Aminotransferase, alanine Aminotransferase, aspartate Aminotransferase, glutamate-glyoxylate Aminotransferase, ornithine-keto acid Aminotransferase, serine-glyoxylate Ammonia... 

The enzymes utilizing serine as amino donor and glyoxylate as amino acceptor are considered together here. Much attention has been paid to these aminotransferases, with the role of these enzymes in photorespiration being a particular focus of interest (see Keys, this volume. Chapter 9). Initial studies on impure extracts indicated the presence of glyoxylate aminotransferases which could use glutamate, aspartate, alanine, and serine as amino donors. The best donor to glyoxylate varied from one tissue to another (Cossins and Sinha, 1965). Leaf peroxisomes were subsequently shown to... 

D-serine [125] and serine, as well as glyoxylate aminotransferase (SGAT)-catalyzed synthesis from L-serine and glyoxylic acid [124], have been reported. 

This enzyme [EC 2.6.1.44] catalyzes the reversible, pyri-doxal-phosphate-dependent reaction of alanine with gly-oxylate to generate pyruvate and glycine. One component of the animal enzyme can utilize 2-oxobutanoate as a substrate instead of glyoxylate. A second component of the enzyme can also catalyze the reaction of alanine with 3-hydroxypyruvate to produce pyruvate and serine. See SerineiPyruvate Aminotransferase... 

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