Sucrose-P synthase

Sucrose-P synthase (SPS) activity in spinach is regulated at three levels, protein quantity, protein phosphorylation/dephosphorylation, and allosteric control.188,189... 

Hesse, H., Willmitzer, L., and Sonnewald, U. 1995. Goning and expression analysis of sucrose-P synthase from sugar beet Beta vulgaris L.) Mol Gen. Genet. 247, 515-520. 

We studied this problem by examining carbon metabolism in the ear and in the adjacent leaf. In both organs carbohydrate pools were measured in relation to key enzymes of this metabolism sucrose-P-synthase, sucrose-synthase, invertase, ADPgIucose pyrophosphorylase. 

Rubisco activity was measured by radiochemical method and enzyme quantity by immunorocket as in (3). Extracts for Sucrose-P-synthase were desalted on G-25 Sephadex column and the reaction was run as in (3), except that UDP glucose and Fructose 6 P were adjusted to 25 and 10 mM respectively.The spectrophotometric assay was used to measure ADPgIucose pyrophosphorylase (3). Sucrose synthase and neutral invertase were assayed as in (4). 

FIGURE 3. a) Total soluble carbohydrate and sucrose, b) sucrose-P-synthase activty In ear-leaf as a function of time after pollination. 

FIGURE 5. a) Net photosynthesis and b) Sucrose-P-synthase activity of the leaf above ear in plants subjected to ear excision or to elimination of all other leaves... 

Sucrose-P-synthase in the same leaf responded clearly to changes in assimilate demand. It increased rapidly in both treated plants at day 11 but declined below control in ear (-) plants whereas it remained high for 40 days in plants deprived of most of their leaves (fig. 5b). 

The variation of sucrose-P-synthase in the leaf adjacent to the ear parallels the variation of assimilate demand by the ear. Carbon fixation capacities decreased continuously but the degradation of Rubisco is less rapid than other soluble proteins. A close agreement exists between the activity of grain ADP glucose pyrophosphorylase and rate of starch accumulation in the grain. 

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. 

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. 

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]. 

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. 

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. 

Figure 5 Model of phosphorus (P) deficiency-induced physiological changes associated with the release of P-mobilizing root exudates in cluster roots of white lupin. Solid lines indicate stimulation and dotted lines inhibition of biochemical reaction sequences or mclaholic pathways in response to P deliciency. For a detailed description see Sec. 4.1. Abbreviations SS = sucrose synthase FK = fructokinase PGM = phosphoglueomutase PEP = phosphoenol pyruvate PE PC = PEP-carboxylase MDH = malate dehydrogenase ME = malic enzyme CS = citrate synthase PDC = pyruvate decarboxylase ALDH — alcohol dehydrogenase E-4-P = erythrosc-4-phosphate DAMP = dihydraxyaceConephos-phate APase = acid phosphatase.

GEIGENBERGER, P., STITT, M., Sucrose synthase catalyses a readily reversible reaction in vivo in developing potato tubers and other plant systems, Planta, 1991,189, 329-339. 

FIGURE 20-25 Sucrose synthesis. Sucrose is synthesized from UDP-glucose and fructose 6-phosphate, which are synthesized from triose phosphates in the plant cell cytosol by pathways shown in Figures 15-7 and 20-9. The sucrose 6-phosphate synthase of most plant species is allosterically regulated by glucose 6-phosphate and P,. 

Thummler, F. Verma, D.P.S. (1987). Nodulin 100 of soybean is the subunit of sucrose synthase regulated by the availability of free heme in nodules. Journal of Biological Chemistry 262, 14730-6. 

Calderon, P. Pontis, H.G. (1985). Increase of sucrose synthase activity in wheat plants after a chilling shock. Plant Science 42,173-6. 

Fig. 22. Schematic presentation of the enzymatic synthesis of UDP-GalNH2 (33) including cofactor regeneration systems. A nucleoside monophosphate kinase (EC 2.7.7.4), B sucrose synthase (EC 2.4.1.13), C gal-l-P uridyltransferase (EC 2.7.7.12), D phosphoglucomutase (EC 2.7.5.1), E glucose-6-P dehydrogenase (EC 1.1.1.49), F lactate dehydrogenase (EC 1.1.1.27), G pyruvate kinase (EC 2.7.1.40) [319]...

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