title: Sucrose synthase catalyzes the de novo production of ADPglucose linked to starch biosynthesis in heterotrophic tissues of plants.
abstract: By using barley seeds, developmental changes of ADPglucose (ADPG)-producing sucrose synthase (SS) and ADPG pyrophosphorylase (AGPase) have been compared with those of UDPglucose (UDPG), ADPG, sucrose (Suc) and starch contents. Both ADPG-synthesizing SS and AGPase activity patterns were found to correlate well with those of ADPG and starch contents. Remarkably, however, maximal activities of ADPG-synthesizing SS were found to be several fold higher than those of AGPase throughout seed development, the highest rate of starch accumulation being well accounted for by SS. Kinetic analyses of SS from barley endosperms and potato tubers in the Suc cleavage direction showed similar K(m) values for ADP and UDP, whereas apparent affinity for Suc was shown to be higher in the presence of UDP than with ADP. Moreover, measurements of transglucosylation activities in starch granules incubated with purified SS, ADP and [U-(14)C]Suc revealed a low inhibitory effect of UDP. The ADPG and UDPG contents in the transgenic S-112 SS and starch deficient potato mutant [Zrenner et al. (1995) Plant J. 7: 97] were found to be 35% and 30% of those measured in wild-type plants, whereas both glucose-1-phosphate and glucose-6-phosphate contents were found to be normal as compared with those of wild-type plants. The overall results thus strongly support a novel gluconeogenic mechanism reported previously [Pozueta-Romero et al. (1999) CRIT: Rev. Plant Sci. 18: 489] wherein SS catalyses directly the de novo production of ADPG linked to starch biosynthesis in heterotrophic tissues of plants.
authors.affiliation: Instituto de Agrobiotecnología y Recursos Naturales, Universidad Pública de Navarra/Consejo Superior de Investigaciones Científicas, Ctra. Mutilva s/n, 31192, Mutilva Baja, Navarra, Spain.
authors.forename: Edurne
authors.initials: E
authors.lastname: Baroja-Fernández
authors.forename: Francisco José
authors.initials: FJ
authors.lastname: Muñoz
authors.forename: Takayo
authors.initials: T
authors.lastname: Saikusa
authors.forename: Milagros
authors.initials: M
authors.lastname: Rodríguez-López
authors.forename: Takashi
authors.initials: T
authors.lastname: Akazawa
authors.forename: Javier
authors.initials: J
authors.lastname: Pozueta-Romero
mesh_terms: D000245:Adenosine Diphosphate Glucose / Q000096:biosynthesis*; D051599:Glucose-1-Phosphate Adenylyltransferase; D019298:Glucose-6-Phosphate / Q000096:biosynthesis; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism*; D001467:Hordeum / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D008969:Molecular Sequence Data; D009713:Nucleotidyltransferases / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018547:Plant Stems / Q000201:enzymology / Q000254:growth & development; D030821:Plants, Genetically Modified; D012639:Seeds / Q000201:enzymology / Q000254:growth & development; D011198:Solanum tuberosum / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D013213:Starch / Q000096:biosynthesis*; D013395:Sucrose / Q000378:metabolism; D014532:Uridine Diphosphate Glucose / Q000096:biosynthesis
chemical_list: D010940:Plant Proteins; D000245:Adenosine Diphosphate Glucose; D019298:Glucose-6-Phosphate; D013395:Sucrose; D013213:Starch; D005964:Glucosyltransferases; C022699:sucrose synthase; D009713:Nucleotidyltransferases; D051599:Glucose-1-Phosphate Adenylyltransferase; D014532:Uridine Diphosphate Glucose