Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.4.1.14 (SPS)
 813 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The constitutive cytosolic expression of a yeast ( Saccharomyces cerevisiae ) invertase within potato ( Solanum tuberosum ) tubers has previously been documented to produce a dramatic metabolic phenotype in which glycolysis, respiration and amino acid synthesis are markedly enhanced at the cost of starch synthesis. These transgenic lines were further characterised by a massive cycle of sucrose degradation and resynthesis via sucrose-phosphate synthase. We have recently developed a B33 patatin driven alc gene construct allowing tight chemical control of gene expression following supply of acetaldehyde with minimal pleiotropic effects of the inducing agent on metabolism. This construct was used for chemical induction of the yeast invertase gene after 10-weeks growth to dissect the complex metabolic phenotype obtained after constitute expression. Inducible expression led to increased invertase activity within 24 h in well-defined areas within growing tubers. Although the sucrose levels were reduced, there was no effect on the levels of starch whilst levels of many amino acids decreased. Labelling experiments revealed that these lines exhibited increased rates of sucrose cycling, whereas rates of glycolysis and of starch synthesis were not substantially changed. From these results we conclude that sucrose cycling is stimulated in response to a short-term increase in the rate of sucrose mobilisation, providing evidence for a role of sucrose cycling as a buffering capacity that regulates the net rate of sucrose usage. In contrast, the dramatic increase in hexose-phosphate levels and the switch from starch synthesis to respiration seen on the constitutive expression of the invertase was not observed in the inducible lines, suggesting that this is the result of cumulative pleiotropic effects that occurred when the transgene was expressed throughout development.
 ...
PMID:Temporally regulated expression of a yeast invertase in potato tubers allows dissection of the complex metabolic phenotype obtained following its constitutive expression. 1560 30

Sucrose-phosphatase (SPP) catalyzes the final step in the pathway of sucrose biosynthesis in both plants and cyanobacteria, and the SPPs from these two groups of organisms are closely related. We have crystallized the enzyme from the cyanobacterium Synechocystis sp PCC 6803 and determined its crystal structure alone and in complex with various ligands. The protein consists of a core domain containing the catalytic site and a smaller cap domain that contains a glucose binding site. Two flexible hinge loops link the two domains, forming a structure that resembles a pair of sugar tongs. The glucose binding site plays a major role in determining the enzyme's remarkable substrate specificity and is also important for its inhibition by sucrose and glucose. It is proposed that the catalytic reaction is initiated by nucleophilic attack on the substrate by Asp9 and involves formation of a covalent phospho-Asp9-enzyme intermediate. From modeling based on the SPP structure, we predict that the noncatalytic SPP-like domain of the Synechocystis sucrose-phosphate synthase could bind sucrose-6(F)-phosphate and propose that this domain might be involved in metabolite channeling between the last two enzymes in the pathway of sucrose synthesis.
 ...
PMID:The structure of a cyanobacterial sucrose-phosphatase reveals the sugar tongs that release free sucrose in the cell. 1593 30

As measured 7, 14, and 21 days after the application of 10(-2) M vanadyl sulfate solution to the foliage of 4.5-month-old sugar beet plants, significantly less growth of the leaves and an increase in the sucrose content of the storage root resulted. Accompanying these alterations were a higher rate of carbon dioxide fixation, a lower rate of respiration, and a decreased rate of nitrate reductase, glutamic-pyruvic transaminase, phosphatase, and invertase activity. The enzymes of sucrose synthesis, sucrose synthetase, sucrose phosphate synthetase and uridine diphosphate glucose-pyrophosphorylase were stimulated. The content of reducing sugar, nitrite N, amino acids and protein was less, and that of nitrate N was greater in the vanadium-treated plants. In the majority of cases the greatest magnitude of change occurred during the first 7 days following treatment. The changes in growth and chemical composition are believed to be closely related to the stimulation or inhibition of the various enzymes by vanadyl sulfate.
 ...
PMID:Effect of Vanadium on Growth, Chemical Composition, and Metabolic Processes of Mature Sugar Beet (Beta vulgaris L.) Plants. 1665 5

Several physiological processes were studied during sugar beet root development to determine the cellular events that are temporally correlated with sucrose storage. The prestorage stage was characterized by a marked increase in root fresh weight and a low sucrose to glucose ratio. Carbon derived from (14)C-sucrose accumulation was partitioned into protein and structural carbohydrate fractions and their amino acid, organic acid, and hexose precursors. The immature root contained high soluble acid invertase activity (V(max) 20 micromoles per hour per milligram protein; K(m) 2 to 3 millimolar) which disappeared prior to sucrose storage. Sucrose storage was characterized by carbon derived from (14)C-sucrose uptake being partitioned into the sucrose fraction with little evidence of further metabolism. The onset of storage was accompanied by the appearance of sucrose synthetase activity (V(max) 12 micromoles per hour per milligram protein; K(m) 7 millimolar). Neither sucrose phosphate synthetase nor alkaline invertase activities were detected during beet development. Intact sugar beet plants (containing a 100-gram beet) exported 70% of the translocate to the beet, greater than 90% of which was retained as sucrose with little subsequent conversions.
 ...
PMID:Sucrose translocation and storage in the sugar beet. 1666 Aug 21

High irradiance-acclimated soybean leaves had the same CO(2) exchange rates, but lower starch accumulation rates and correspondingly higher translocation rates than unacclimated leaves. Increased translocation rates were associated with increased sucrose phosphate synthetase (EC 2.4.1.14) activity. Foliar sucrose levels and adenosine diphosphate-glucose pyrophosphorylase (EC 2.7.7.9) activity were unaffected. Carbon assimilation, partitioning, and enzyme activity of unacclimated leaves were unaltered even after a second day's exposure to high irradiance. Results are consistent with the hypothesis that photosynthate partitioning between starch synthesis and sucrose translocation are controlled in part by the rate of sucrose synthesis.
 ...
PMID:Photosynthate partitioning in soybean leaves at two irradiance levels: comparative responses of acclimated and unacclimated leaves. 1666 Oct 72

Conversion of [(14)C]galactose (Gal) 1-P, UDP-[(14)C]Gal, or UDP-[(14)C]glucose to [(14)C]sucrose was observed when cell-free homogenates of cucumber (Cucumis sativus L.) fruit peduncles were incubated with individual (14)C-labeled substrates, appropriate cofactors, and fructose. The sucrose product was labeled only in the glucose moiety. Conversion of [(14)C]Gal-1-P to [(14)C]sucrose was catalyzed by extracts of peduncles from all other stachyose transporting species tested, as well as green bean (a sucrose transporter) but was not catalyzed by peduncle extracts from three other sucrose transporting species. In cucumber, the ability of extracts to form [(14)C]sucrose from [(14)C]Gal-1-P was greater when peduncles were harvested from growing fruit than from unpollinated ovaries. [(14)C]Sucrose formation from [(14)C]Gal-1-P was inhibited by Mg . PPi, Mg . UDP, UMP, and sucrose. alpha-Galactosidase, galactokinase, UDP-gal pyrophosphorylase, UDP-Gal-4'-epimerase, UDP-glucose pyrophosphorylase, and sucrose synthase activities were detected in peduncle extracts. Neither sucrose phosphate synthetase nor hexose-1-P uridyltransferase were detected. Peduncle tissue contained a small pool of free galactose. These results suggest a potential pathway for the metabolism of galactose moieties hydrolyzed from stachyose, the major sugar transported by cucumber plants.
 ...
PMID:A Potential Pathway for Galactose Metabolism in Cucumis sativus L., A Stachyose Transporting Species. 1666 41

Experiments were conducted with soybean (Glycine max [L.] Merr. cv ;Ransom') plants to determine if diurnal rhythms in net carbon dioxide exchange rate (CER), stomatal resistance, and sucrose-phosphate synthase (SPS) activity persisted in constant environmental conditions (constant light, LL; constant dark DD) and to assess the importance of these rhythms to the production of nonstructural carbohydrates (starch, sucrose, and hexose). Rhythms in CER, stomatal resistance, and SPS activity were observed in constant environmental conditions but the rhythms differed in period length, amplitude, and phase. The results indicated that these photosynthetic parameters are not controlled in a coordinated manner. The activity of UDPG pyrophosphorylase, another enzyme involved in sucrose formation, did not fluctuate rhythmically in constant conditions but increased with time in plants in LL. In LL, the rhythm in CER was correlated positively with fluctuations in total chlorophyll (r = 0.810) and chlorophyll a (r = 0.791) concentrations which suggested that changes in pigment concentration were associated with, but not necessarily the underlying mechanism of, the rhythm in photosynthetic rate. Assimilate export rate, net starch accumulation rate, and leaf sucrose concentration also fluctuated in constant light. No single photosynthetic parameter was closely correlated with fluctuations in assimilate export during LL; thus, assimilate export may have been controlled by interactions among the endogenous rhythms in CER, SPS activity, or other metabolic factors which were not measured in the present study.
 ...
PMID:Endogenous Rhythms in Photosynthesis, Sucrose Phosphate Synthase Activity, and Stomatal Resistance in Leaves of Soybean (Glycine max [L.] Merr.). 1666 41

In fully expanded leaves of greenhouse-grown cotton (Gossypium hirsutum L., cv Coker 100) plants, carbon export, starch accumulation rate, and carbon exchange rate exhibited different behavior during the light period. Starch accumulation rates were relatively constant during the light period, whereas carbon export rate was greater in the afternoon than in the morning even though the carbon exchange rate peaked about noon. Sucrose levels increased throughout the light period and dropped sharply with the onset of darkness; hexose levels were relatively constant except for a slight peak in the early morning. Sucrose synthase, usually thought to be a degradative enzyme, was found in unusually high activities in cotton leaf. Both sucrose synthase and sucrose phosphate synthetase activities were found to fluctuate diurnally in cotton leaves but with different rhythms. Diurnal fluctuations in the rate of sucrose export were generally aligned with sucrose phosphate synthase activity during the light period but not with sucrose synthase activity; neither enzyme activity correlated with carbon export during the dark. Cotton leaf sucrose phosphate synthase activity was sufficient to account for the observed carbon export rates; there is no need to invoke sucrose synthase as a synthetic enzyme in mature cotton leaves. During the dark a significant correlation was found between starch degradation rate and leaf carbon export. These results indicate that carbon partitioning in cotton leaf is somewhat independent of the carbon exchange rate and that leaf carbon export rate may be linked to sucrose formation and content during the light period and to starch breakdown in the dark.
 ...
PMID:Diurnal fluctuations in cotton leaf carbon export, carbohydrate content, and sucrose synthesizing enzymes. 1666 60

Levels of fructose 2,6-bisphosphate (F2,6BP) and related metabolites were measured in 8- or 9-day-old barley (Hordeum vulgare L.) primary leaves throughout a 24 hour cycle. Young barley leaves contained about 0.4 nanomole F2,6BP per milligram chlorophyll at the end of a 12 hour dark period. F2,6BP levels increased rapidly following a dark-to-light transition and then decreased to about 0.1 nanomole per milligram chlorophyll after 5 or 10 minutes of light. Low levels of F2,6BP were detected in barley primary leaves throughout the day. A 10-fold increase in F2,6BP was observed during the first hour of the dark period and then levels of this metabolite decreased slowly for the next several hours. Only small diurnal fluctuations were noted in barley leaf glucose 6-phosphate and uridine 5'-diphosphoglucose levels. There were rapid changes in whole leaf F2,6BP levels when the light intensity was altered. High F2,6BP levels in the dark were not observed after short photosynthetic periods. Results obtained with barley primary leaves support the suggestion that F2,6BP is involved in regulating the flow of photosynthate from the chloroplast to sucrose. Extractable sucrose-phosphate synthase activity was inversely related to barley primary leaf F2,6BP levels. This finding may indicate that the activities of sucrose-phosphate synthase and cytosolic fructose 1,6-bisphosphatase in barley primary leaves are metabolically coordinated.
 ...
PMID:Control of photosynthetic sucrose synthesis in barley primary leaves: role of fructose 2,6-bisphosphate. 1666 83

The effect of inorganic phosphate (Pi) on sucrose-phosphate synthase (SPS) activity was determined for the enzyme from five plant species (Nicotiana tabacum L., Spinacia oleracea L., Triticum aestivum L., Zea mays L., Glycine max L.) using two assay methods. The assay method based on determination of uridine diphosphate glucose- (UDPG) and fructose-6-phosphate-dependent sucrose formation was linear up to 15 minutes for all species tested. When assayed in this way, the effect of Pi at levels of 5 or 10 millimolar in the assay was variable, ranging from 0 to 35% inhibition of SPS activity. The assay method based on substrate dependent UDP formation was linear for some, but not for all of the species tested. Deviations from linearity were caused by loss of UDP from the assay medium. In some species, the extent of UDP loss was influenced by the level of Pi in the assay medium and, for at least one species (tobacco), it was influenced by the environment in which the plants were grown. The results indicated that (a) the role of Pi as an effector of SPS may vary depending on the species, and (b) the UDP assay method should be used with caution for assays of crude or desalted extracts, particularly when evaluating the effect of Pi on SPS activity.
 ...
PMID:Species and Environmental Variations in the Effect of Inorganic Phosphate on Sucrose-Phosphate Synthase Activity : Reliability of Assays Based Upon UDP Formation. 1666 54


<< Previous 1 2 3 4 5 6 7 8 Next >>