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

(1) Partially purified preparations of spinach (Spinacia oleracea L.) leaf sucrose-phosphate synthase (SPS) contain an endogenous protein kinase that phosphorylates and inactivates the enzyme with [gamma-32P]ATP. (2) The kinetic effect of phosphorylation is to alter affinities for substrates and the effector inorganic phosphate without affecting maximum velocity. (3) Two-dimensional peptide mapping of tryptic digests of in vitro labeled SPS yielded two phosphopeptides (designated sites 5 and 7). Labeling of the two sites occurred equally with time, and both correlated with inactivation. Maximum inactivation was associated with incorporation of 1.5 to 2.0 mol P/mol SPS tetramer, and about 70% of the phosphoryl groups were incorporated into one of the sites (phosphopeptide 7). (4) Phosphorylation and inactivation were strongly inhibited by NaCl, and the presence of salt alters some characteristics of the kinase reaction. In the absence of salt, the apparent Km for Mg.ATP was estimated to be 5 microM. (5) The dependence of the rate of phosphorylation on SPS concentration suggested that SPS and the protein kinase are distinct enzymes, but have some tendency to associate especially in the presence of ethylene glycol. (6) Ca2+/EGTA and polyamines have no effect on the rate of phosphorylation, whereas polycations (polylysine, polybrene and protamine) are inhibitory. (7) Of the metabolic intermediates tested, Glc 6-P inhibited phosphorylation and inactivation of the enzyme. The inhibition was not antagonized by inorganic phosphate, which suggests that Glc 6-P may be an effector of the kinase, rather than the target protein. Regulation by Glc 6-P may be of physiological significance.
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PMID:In vitro phosphorylation and inactivation of spinach leaf sucrose-phosphate synthase by an endogenous protein kinase. 182 91

The influence of calcium ions on the electrophoretic properties of phospholipid stabilized emulsions containing various quantities of the sodium salts of oleic acid (SO), phosphatidic acid (SPA), phosphatidylinositol (SPI), and phosphatidylserine (SPS) was examined. The critical flocculation concentration of calcium corresponded to a critical zeta potential in all but one of the systems. Systems of approximately equal zeta potential in 0 mM Ca++ had different zeta potentials in dilute solutions of Ca++. A comparison of emulsions of similar polydispersity suggests that these differences may be largely related to differences in particle size and surface area of the emulsions. The influence of Ca++ on the monolayer properties of mixed films containing phosphatidylcholine (PC) with either SPA or SO was also examined at the air-water interface. Films containing PC with SPA were more expanded on a subphase containing calcium compared to a subphase with no calcium. In addition, the compression of films containing PC with SO demonstrated two collapse pressures while SPA was relatively more miscible in the film. This suggests that phase separation of interfacial lipids occurs more easily in systems containing PC and SO. These results may help to explain differences in the flocculation and coalescence of emulsions stabilized by lipid films of different composition.
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PMID:The influence of charged lipids on the flocculation and coalescence of oil-in-water emulsions. II: Electrophoretic properties and monolayer film studies. 225 Feb

Analysis of Ag specificity of TRC-gamma delta+ T cells in humans has been hampered by the fact that cloned lines of these cells expanded in IL-2 generally display high NK-like cytotoxic activity. A TCR-gamma delta+ CTL clone, isolated in IL-4, strongly lysed a specific stimulator cell, the EBV-transformed cell line JY, but failed to lyse K562 and other target cells sensitive for NK cell activity. Subsequent culture of this clone (CD124) in IL-2 induced high cytotoxic activity against the NK sensitive target cells. K562 cells were unable to induce the secretion of N alpha-benzyloxycarbonyl-L-lysine thiobenzyl ester [(BLT)-serine esterase] or influx of Ca2+ ions in clone CD124 cultured in either IL-4 or IL-2. In contrast, JY cells induced high BLT-serine esterase secretion and an increase of cytosolic Ca2+ levels. By using a combination of a 51Cr-release assay and a BLT-serine esterase secretion assay, the reactivity of clone CD124 against a limited number of target cells was analyzed. CD124 which expresses HLA-A2 and -B7, recognized an Ag shared by JY (HLA-A2; B7; C blank; DR4,6) and one haplotype expressed by the cell line SPS (HLA-A1; B14; Cw6; DR4). The only specificity shared by SPS and JY was HLA-DR4. However, clone CD124 failed to lyse 5 other HLA-DR4+ target cells. The cytotoxic activity of clone CD124 was inhibited by the class I MHC specific mAb W6/32 and the anti-beta 2m mAb A88, but not, or only marginally, by the anti HLA-DQ mAb SPV-L3 or the anti-HLA-DR mAb 135. These data strongly suggest that clone CD124 recognizes a class I MHC Ag different from HLA-A, -B, or -C.
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PMID:Antigen-specific, but not natural killer, activity of T cell receptor-gamma delta cytotoxic T lymphocyte clones involves secretion of N alpha-benzyloxycarbonyl-L-lysine thiobenzyl ester serine esterase and influx of Ca2+ ions. 247 1

1. The links between behavioural state, gross electrophysiology and the activity of neurons and astrocytes are reviewed to stimulate interest in the contributions that glia make to behaviour. 2. Behavioural arousal in which neuronal responsivity ("sensitivity") is elevated is also associated with a sustained (0.5-10 sec) potential shift (SPS). 3. There is powerful and accumulating evidence that the SPS is primarily of glial origin. 4. In epilepsy neurons are hyperactive and there is a massive SPS during seizures. In seizure free periods, epileptic animals frequently have elevated arousal responses and increased neuronal sensitivity, indicating that seizures may be due to elevation of the activity of a normally adaptive sensitizing mechanism. 5. The common finding of an astrocytic pathology in epilepsy and the links between arousal, neuronal sensitization, SPSs and seizures implicates a modulatory role for astrocytes in both health and disease. 6. Glia, especially astrocytes, may modulate neuronal responsiveness by regulation of the microenvironment. 7. At the current state of knowledge, regulation of extracellular ionic K+, Ca2+ and neurotransmitter glutamate and GABA seem to be the most important candidates for modulating neuronal sensitivity in arousal and abnormally for seizure genesis. 8. Both in phylogeny and in ontogeny, glia and neurons have intimate associations. 9. The functional astrocytic syncitium is in a prime position to control the ecology of neuronal populations and thereby their activity. 10. The physiology and biochemistry of glia-neuronal interactions offers exciting new prospects for developments in behavioural neuroscience.
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PMID:Do glia contribute to behaviour? A neuromodulatory review. 257 39

Plant 3-hydroxy-3-methylglutaryl-CoA reductase(HMGR; EC 1.1.1.34) and sucrose-phosphate synthase (SPS; EC 2.4.1.14) and synthetic peptides designed from the known phosphorylation sites of plant HMGR (SAMS*: KSHMKYNRSTKDVK), rat acetyl-CoA carboxylase (SAMS: HMRSAMSGLHLVKRR), spinach SPS (SP2: GRRJRRISSVEJJDKK), and spinach NADH:nitrate reductase (NR6: GPTLKRTASTPFJNTTSK) were used to characterize kinase activities from cauliflower (Brassica oleracea L. ) inflorescences. The three major peaks of protein kinase activity resolved by anion-exchange FPLC are homologs of those observed previously in spinach leaves and thus are designated PKI, PKIV, and PKIII, listed in order of elution. PKIV was the most active in terms of phosphorylation and inactivation of recombinant Nicotiana HMGR and was also strictly Ca2+ dependent. The novel aspects are that PKIII has not been detected in previous cauliflower studies, that SAMS* is a more specific peptide substrate to identify potential HMGR kinases, and that the major HMGR kinase in cauliflower is Ca2+ dependent. Of the three major kinases that phosphorylated the SP2 peptide only PKI (partially Ca2+ sensitive) and PKIII (Ca2+ insensitive) inactivated native spinach leaf SPS. Cauliflower extracts contained endogenous SPS that was inactivated by endogenous kinase(s) in an ATP-dependent manner and this may be one of the substrate target proteins for PKI and/or PKIII. The substrate specificity of the three kinase peaks was studied using synthetic peptide variants of the SP2 sequence. All three kinases had a strong preference for peptides with a basic residue at P-6 (as in SP2 and SAMS*; SAMS has a free amino terminus at this position) or a Pro at P-7 (as in NR6). This requirement for certain residues at P-6 or P-7 was not recognized in earlier studies but appears to be a general requirement. In plant HMGR, a conserved His residue at P-6 is involved directly in catalysis and this may explain why substrates reduced HMGR phosphorylation in vitro.
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PMID:3-Hydroxy-3-methylglutaryl-coenzyme A reductase kinase and sucrose-phosphate synthase kinase activities in cauliflower florets: Ca2+ dependence and substrate specificities. 967 40

Far-Western overlays of soluble extracts of cauliflower revealed many proteins that bound to digoxygenin (DIG)-labelled 14-3-3 proteins. Binding to DIG-14-3-3s was prevented by prior dephosphorylation of the extract proteins or by competition with 14-3-3-binding phosphopeptides, indicating that the 14-3-3 proteins bind to phosphorylated sites. The proteins that bound to the DIG-14-3-3s were also immunoprecipitated from extracts with anti-14-3-3 antibodies, demonstrating that they were bound to endogenous plant 14-3-3 proteins. 14-3-3-binding proteins were purified from cauliflower extracts, in sufficient quantity for amino acid sequence analysis, by affinity chromatography on immobilised 14-3-3 proteins and specific elution with a 14-3-3-binding phosphopeptide. Purified 14-3-3-binding proteins included sucrose-phosphate synthase, trehalose-6-phosphate synthase, glutamine synthetases, a protein (LIM17) that has been implicated in early floral development, an approximately 20 kDa protein whose mRNA is induced by NaCl, and a calcium-dependent protein kinase that was capable of phosphorylating and rendering nitrate reductase (NR) sensitive to inhibition by 14-3-3 proteins. In contrast to the phosphorylated NR-14-3-3 complex which is activated by dissociation with 14-3-3-binding phosphopeptides, the total sugar-phosphate synthase activity in plant extracts was inhibited by up to 40% by a 14-3-3-binding phosphopeptide and the phosphopeptide-inhibited activity was reactivated by adding excess 14-3-3 proteins. Thus, 14-3-3 proteins are implicated in regulating several aspects of primary N and C metabolism. The procedures described here will be valuable for determining how the phosphorylation and 14-3-3-binding status of defined target proteins change in response to extracellular stimuli.
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PMID:Phosphorylation-dependent interactions between enzymes of plant metabolism and 14-3-3 proteins. 1034 39

Despite 14-3-3 proteins being implicated in the control of the eukaryotic cell cycle, metabolism, cell signalling and survival, little is known about the global regulation or functions of the phosphorylation-dependent binding of 14-3-3s to diverse target proteins. We identified Arabidopsis cytosolic proteins that bound 14-3-3s in competition with a 14-3-3-binding phosphopeptide, including nitrate reductase, glyceraldehyde- 3-phosphate dehydrogenase, a calcium-dependent protein kinase, sucrose-phosphate synthase (SPS) and glutamyl-tRNA synthetase. Remarkably, in cells starved of sugars or fed with non-metabolizable glucose analogues, all 14-3-3 binding was lost and the target proteins were selectively cleaved into proteolytic fragments. 14-3-3 binding reappeared after several hours of re-feeding with sugars. Starvation-induced degradation was blocked by 5-amino imidazole-4-carboxamide riboside (which is converted to an AMP-mimetic) or the protease inhibitor MG132 (Cbz-leu-leu-leucinal). Extracts of sugar-starved (but not sugar-fed) Arabidopsis cells contained an ATP-independent, MG132-sensitive, neutral protease that cleaved Arabidopsis SPS, and the mammalian 14-3-3-regulated transcription factor, FKHR. Cleavage of SPS and phosphorylated FKHR in vitro was blocked by binding to 14-3-3s. The finding that 14-3-3s participate in a nutrient-sensing pathway controlling cleavage of many targets may underlie the effects of these proteins on plant development.
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PMID:14-3-3s regulate global cleavage of their diverse binding partners in sugar-starved Arabidopsis cells. 1085 32

Detached ears of sorghum (Sorghum vulgare) were cultured in complete liquid medium containing Ca2+(0, 3, 10 and 30 mM) and effect of this ion on the conversion of sucrose to starch with respect to the activities of amylases, sucrose synthase, sucrose phosphate synthase and soluble invertases were studied in developing grains. Presence of 3 mM Ca2+ in culture medium enhanced both accumulation of starch and activity of alpha-amylase in grain but without having any influence on the activity of beta-amylase. However, with 10 and 30 mM Ca2+, the accumulation of starch and activities of both amylases decreased and with advancement in culturing period, starch accumulation was further decreased. Irrespective of its concentration, Ca2+ enhanced the activities of sucrose synthase (synthesis), sucrose-phosphate synthase, soluble acid invertase and soluble-neutral invertase. Increase in the concentration of Ca2+ in culture medium was concomitant with an elevation in relative proportion of sucrose in the grain reflecting a net balance in per cent increase with Ca2+ in the activities of sucrose-synthesizing enzymes over sucrose-hydrolysing ones. Based on the results, it is suggested that assimilation of Ca2+ by grain is essential for maintaining high activity of alpha-amylase to generate starch primers required for the conversion of sucrose to starch during grain filling in sorghum.
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PMID:Calcium-mediated conversion of sucrose to starch in relation to the activities of amylases and sucrose-metabolizing enzymes in sorghum grains raised through liquid culture. 1098 25

A protein kinase activity that can phosphorylate and inactivate rice (Oryza sativa) sucrose-phosphate synthase (SPS; UDP-glucose: d-fructose-6-phosphate-2-glucosyl transferase, EC 2.4.1.14) was measured in extracts prepared from leaves exposed to light-dark transitions. Enzyme activity present in extracts from dark leaves was about 5-fold higher than the activity in extracts from leaves that had been collected in the light. The protein kinase (named R-SPSK) was purified about 100-fold from dark leaves and its biochemical properties were studied. The micromolar dependence of Ca2+ exhibited by R-SPSK, and its response to calmodulin antagonists was similar to the properties associated with members of the plant Calcium-Dependent Protein Kinase (CDPK) family. Two modulators of SPS activity, Pi and Glc-6-P, were examined for an effect on R-SPSK. While Glc-6-P did not affect R-SPSK activity, Pi drastically increased the kinase activity. Taken together, these data provide evidence that SPS may be regulated by a CDPK type protein-kinase whose activity is modulated by light-dark transitions and stimulated by Pi, the negative effector of SPS activity.
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PMID:A CDPK type protein kinase is involved in rice SPS light modulation. 1206 Feb 34

The regulation of sucrose-phosphate synthase (SPS) and nitrate reductase (NR) activities from mature spinach (Spinacia oleracea L.) leaves share many similarities in vivo and in vitro. Both enzymes are light/dark modulated by processes that involve, at least in part, reversible protein phosphorylation. Experiments using desalted crude extracts show that the ATP-dependent inactivation of spinach SPS and NR is sensitive to inhibition by glucose-6-phosphate. Also, a synthetic peptide homolog of the spinach SPS phosphorylation site inhibits the ATP-dependent inactivation of both enzymes with a similar concentration dependence. We have addressed the possibility that SPS and NR are regulated by the same protein kinase by partially purifying the protein kinases involved. Three unique kinase activities can be separated by anion-exchange and size-exclusion chromatography. Each peak of activity has a different substrate specificity. By gel filtration, they have apparent molecular masses of approximately 45, 60, and 150 kD. Additionally, the activities of the two smaller kinases are dependent on micromolar concentrations of Ca2+, whereas the 150-kD kinase is not. Finally, the 150-kD kinase has a subunit molecular mass of about 65 kD as determined by renaturing the kinase activity in situ following sodium dodecyl sulfate-polyacrylamide gel electrophoresis.
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PMID:Spinach Leaf Sucrose-Phosphate Synthase and Nitrate Reductase Are Phosphorylated/Inactivated by Multiple Protein Kinases in Vitro. 1222 28


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