Phosphoserine aminotransferase

Phospholipase Ca Phosphoserine aminotransferase Proteasome 20S or 26S Protein kinase (cdc2-like)... 

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.

Hanford and Davies (1958) showed that a partly purilied extract from pea epicotyls converted phosphoglycerate to phosphoserine. The reaction was dependent on NAD, glutamate, and pyridoxal phosphate. The first step was presumably catalyzed by phosphoglycerate dehydrogenase and the second by glutamate phosphohydroxypyruvate aminotransferase. Such a phosphoserine aminotransferase was present in extracts of pea seeds, leaves, and apical meristems (Cheung et al., 1968). Little is known of phosphoserine phosphatase in plants, but its presence in spinach leaves is reported by Larsson and Albertsson (1979). 

Phosphoglycerate dehydrogenase 2 phosphoserine aminotransferase 3 phosphoserine phosphatase 4 serine hydroxymethyltransferase 5 glycine aminotransferase 6 phosphoglyceromutase, enolase, pyruvate kinase (Fig. 44) 7 alanine oxoacid aminotransferase... 

It is of interest to compare the tertiary structure of AspAT with that of other PLP-dependent enzymes. Some PLP enzymes whose primary structures are quite different from AspAT exhibit similar tertiary structures. Such enzymes are a>-amino acid pyruvate aminotransferase,341 phosphoserine aminotransferase351 and tyrosine-phenol lyase361 (Phillips, R., personal communication). Similarity in tertiary structure among these PLP enzymes may lead to the idea that many PLP-dependent enzymes share the same ancestor protein. There are PLP enzymes belonging to its own category, such as glycogen phosphorylase and tryptophan synthase.37 381 These enzymes do not share any similarities in either primary or tertiary structures with AspAT. 

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