Sucrose-phosphate synthase

TRETHEWEY, R.N., REISMEIER, J.W., WILLMITZER, L., STITT, M GEIGENBERGER, P., Tuber specific expression of a yeast invertase and a bacterial glucokinase in potato leads to an activation of sucrose phosphate synthase and the creation of a futile cycle, Planta, 1999, 208, 227-238. 

REIMHOLZ, R., GEIGER, M., HAAKE, V., DEITING, U., KRAUSE, K.P., SONNEWALD, U., STITT, M., Sucrose phosphate synthase is regulated by metabolites and protein phosphorylation in potato tubers, in a manner analogous to the enzyme in leaves, Planta, 1994,192, 480-488. 

FIGURE 20-27 Regulation of sucrose phosphate synthase by phosphorylation. A protein kinase (SPS kinase) specific for sucrose phosphate synthase (SPS) phosphorylates a Ser residue in SPS, inactivating it a specific phosphatase (SPS phosphatase) reverses this inhibition. The kinase is inhibited allosterically by glucose 6-phosphate, which also activates SPS allosterically. The phosphatase is inhibited by Pi, which also inhibits SPS directly. Thus when the concentration of glucose 6-phosphate is high as a result of active photosynthesis, SPS is activated and produces sucrose phosphate. A high P, concentration, which occurs when photosynthetic conversion of ADP to ATP is slow, inhibits sucrose phosphate synthesis. 

Huber, S.C. Huber, J.L. (1996) Role and regulation of sucrose-phosphate synthase in higher plants. Annu. Rev. Plant Physiol. Plant Mol. Biol. 47, 431-444. 

FIGURE 10.20 The action of fructan 1-exohydrolase and fructan fructan 1-fructosyltransferase in dormant and sprouting tubers on inulin depolymerization. Abbreviations 1-feh = fructan 1-exohydrolase 1-fft = fructan fructan 1-fructosyltransferase hk = hexokinase spp = sucrose phosphate phosphatase sps = sucrose phosphate synthase GF = sucrose G = glucose F = fructose GFF = 1-ketose GF-P = sucrose phosphate UDP-G = uridine diphosphate glucose F-6-P = fructose-6-phosphate. 

Some of the triose phosphate available for product synthesis will be transported into the cytosol and converted into sucrose (Fig. 2). In both photosynthetic and nonphotosynthetic cells, sucrose is synthesized via sucrose phosphate synthase, which catalyses the reaction... 

It is worth noting that the two sucrose metabolizing enzymes, sucrose synthase and sucrose-phosphate synthase, were both discovered by Leloir and Cardini (1955) (see Preface ). 

Ohsugi, R., and Huber, S. C. 1987. Light modulation and localization of sucrose phosphate synthase activity between mesophyll cells and bundle sheath cells in C4 species. Plant Physiol. 84, 1096-1101. 

After glucose synthesis in photosynthesis, the disaccharide sucrose (a-D-Glc(l —> 2)(3-D-Fru) is used as a readily transportable sugar. Sucrose synthesis successively involves the following UDP-glucose + fructose-6-phosphate —> sucrose-6-phosphate + UDP [via sucrose phosphate synthase] sucrose-6-phosphate + H20 —> sucrose + P [via sucrose-6-phosphatase]. 

Sucrose-phosphate synthase SpsA Synechocystis sp. D90911 61... 

Zhu, Y.J., Komor, E., and Morre, P.H., Sucrose accumulation in the sugarcane stem is regulated by the difference between the activities of soluble acid invertase and sucrose phosphate synthase. Plant Physiol., 115, 609, 1997. 

Glucose 6-phosphate/phobphate translotator 76 Sucrose-phosphate synthase 116... 

VALDEZ-ALARCON, J.J., FERRANDO, M., SALERNO, G., JIMENEZ-MORAILA, B., HERRERA-ESTRELLA, L., Characterization of a rice sucrose-phosphate synthase-encoding gene, Gene, 1996,170,217-222. 

Figure 4. Extractable activity of sucrose-phosphate synthase from control (open bars) and mildly water stressed leaves of Phaseobis vulgaris var Linden. Data from Vassey and Sharkey 1989).

So the CO2 and O2 g insensitivity observed in water stressed plants indicates an effect on the biochemistry of photosynthesis, and from the analytical gas exchange analysis presented above, it is predicted that the effect is on sucrose or starch synthesis, or both. Vassey and Sharkey (11) found that the extractable activity of sucrose-phosphate synthase (SPS) was reduced by nearly 70% by mild water stress (Figure 4). We have made a number of additional tests and have been able to demonstrate the following 1. SPS in water stressed plants recovers when the plant is placed in high CO2 (1 mbar) even though the stress is not relieved. 2. Unstressed plants held in a low CO2 (75 /ibar) environment for one hour exhibit reduced SPS activity. 3. The recovery of SPS activity in water stressed plants requires one to five hours and can be prevented by feeding cycloheximide. 

ICrapp A. and Stitt M. 1995. An evaluation of direct and indirect mechanisms for the sink regulation of photosynthesis in spinach change in gas exchange, carbohydrates, metabohtes, enzyme activities and steady-state transcript levels after cold-girdling source leaves. Planta 195 313-323. Krause K.P. and Stitt M. 1992. Sucrose-6-phosphate levels in spinach leaves and their effects on sucrose-phosphate synthase. Phytochemistry 31 1143-1146. 

Glc (Hill et al. 1995). Cycling between hexoses and the triose phosphates is catalyzed by pyrophosphate Fru-6-phosphate 1 -phosphotransferase [PFK(PPi)], and this is the most active phosphofructokinase in secondary wall stage cotton fibers (Waffler and Meier 1994). The activity of PFK(PPi) would also consume PPi released by UDP-Glc pyrophosphorylase acting in the synthetic direction (Delmer 1999) to generate the UDP-Glc required by sucrose phosphate synthase (SPS see below). 

A ROLE FOR SUCROSE PHOSPHATE SYNTHASE IN INTRAFIBER CELLULOSE SYNTHESIS... 

Babb V.M. and Haigler C.H. 2001. Sucrose phosphate synthase activity rises in correlation with high-rate cellulose synthesis in three heterotrophic systems. Plant Physiol 127 1234-1242. 

Hauch S. and Magel E. 1998. Extractable activities and protein content of sucrose-phosphate synthase, sucrose synthase, and neutral invertase in trunk tissue of Robiniapseudoacacia L. are related to cambial wood production and heartwood formation. Planta 207 266-274. 

Schrader S. and Sauter J.J. 2002. Seasonal changes of sucrose-phosphate synthase and sucrose synthase activities in poplar wood (Populm x Canadensis Moench robusta) and their possible role in carbohydrate metabolism. J Plant Physiol 159 833-843. 

Tummala J. 1996. Response of sucrose phosphate synthase activity to cool temperatures in cotton. M.S. thesis, Texas Tech University, Lubbock, TX. 

---