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PubMed1975

Hybridization of polymers of antibiotic C-nucleoside phosphates, poly(formycin phosphate) and poly(laurusin phosphate)

The ability of complex formation of poly-(formycin phosphate), poly(F), and poly(laurusin phosphate), poly(L), with the polymers of natural polynucleotides was examined mainly by mixing experiments in 0.1 M NaCl-0.05 M sodium cascodylate buffer (pH 7.0) at 2 degrees. Poly(F) formed complexes with poly(U) and poly(I) in the ratio of 1:1 and 1:2, respectively. Poly(L) formed complexes with poly(A) in 2:1 ration and poly(C) in 1:2 and 2:1 ratios in addition to a self-complex. Poly(F) and poly(L) also formed a 1:2 complex between them. Some of these complexes were assumed to contain novel types of base pairings using the 7-NH group. Thus it was concluded that poly(L) could form complexes with both, the oligomer of cycloadenylic acid (øcn-120 degrees) and polymers of natural nucleotides (øcn0degrees), showing flexibility of the torsion angle of the laurusin residue.

Adenosine Monophosphate↗
PubMed1997

ATP-dependent choline phosphate-induced mitogenesis in fibroblasts involves activation of pp70 S6 kinase and phosphatidylinositol 3'-kinase through an extracellular site. Synergistic mitogenic effects of choline phosphate and sphingosine 1-phosphate.

In serum-starved NIH 3T3 clone 7 fibroblasts, choline phosphate (ChoP) (0.5-1 mM) and insulin synergistically stimulate DNA synthesis. Here we report that ATP also greatly enhanced the mitogenic effects of ChoP (0.1-1 mM) both in the absence and presence of insulin; maximal potentiating effects required 50-100 microM ATP. The co-mitogenic effects of ATP were mimicked by adenosine 5'-O-(3-thiotriphosphate), adenosine 5'-O-(2-thiodiphosphate), ADP, and UTP, but not by AMP or adenosine, indicating the mediatory role of a purinergic P2 receptor. Externally added ChoP acted on DNA synthesis without its detectable uptake into fibroblasts, indicating that ChoP can be a mitogen only if it is released from cells. Extracellular ATP (10-100 microM) induced extensive release of ChoP from fibroblasts. ChoP had negligible effects, even in the presence of ATP or insulin, on the activity state of p42/p44 mitogen-activated protein kinases, while in combination these agents stimulated the activity of phosphatidylinositol 3'-kinase (PI 3'-kinase). Expression of a dominant negative mutant of the p85 subunit of PI 3'-kinase or treatments with the PI 3'-kinase inhibitor wortmannin only partially (approximately 40-50%) reduced the combined effects of ChoP, ATP, and insulin on DNA synthesis; in contrast, the pp70 S6 kinase inhibitor rapamycin almost completely inhibited these effects. ATP and insulin also potentiated, while rapamycin strongly inhibited, the mitogenic effects of sphingosine 1-phosphate (S1P). Furthermore, even maximally effective concentrations of ChoP and S1P synergistically stimulated DNA synthesis. The results indicate that in the presence of extracellular ATP and/or S1P, ChoP induces mitogenesis through an extracellular site by mechanisms involving the activation of pp70 S6 kinase and, to a lesser extent, PI 3'-kinase.

3T3 Cells↗
PubMed1980

Biochemical genetics of the pentose phosphate cycle: human ribose 5-phosphate isomerase (RPI) and ribulose 5-phosphate 3-epimerase (RPE).

1. Staining procedures are described for the detection after starch-gel electrophoresis of ribose-5-phosphate isomerase (RPI) and ribulose 5-phosphate 3-epimerase (RPE). 2. Both RPI and RPE were detected in all human tissues including red cells, lymphocytes and fibroblasts. 3. No evidence was found for more than one structural gene locus for either enzyme. 4. No allelic variants of either enzyme were found in erythrocyte lysates from over 200 unrelated individuals. 5. Preliminary data are presented which suggest that differences in tissue RPE isozyme patterns may be due to endogenous proteolytic activity. 6. Electrophoretic analysis of RPE and RPI isozyme patterns in extracts of man/mouse hybrid cells indicates that RPE is probably a dimer and RPI may also be polymeric.

Animals↗
PubMed1994

Specific activity of skeletal alkaline phosphatase in human osteoblast-line cells regulated by phosphate, phosphate esters, and phosphate analogs and release of alkaline phosphatase activity inversely regulated by calcium.

We assessed the significance of Ca and phosphate (P(i)) as determinants of (1) the amount of skeletal alkaline phosphatase (ALP) activity in SaOS-2 (human osteosarcoma) cells and normal human bone cells, and (2) the release of ALP activity from the cells into the culture medium. After 24 h in serum-free BGJb medium containing 0.25-2 mM P(i), the specific activity of ALP in SaOS-2 cells was proportional to P(i) concentration (r = 0.99, p < 0.001). The P(i)-dependent increase in ALP activity was time dependent (evident within 6 h) and could not be attributed to decreased ALP release, since P(i) also increased the amount of ALP activity released (r = 0.99, p < 0.001). Parallel studies with Ca (0.25-2.0 mM) showed that the amount of ALP activity released from SaOS-2 cells was inversely proportional to the concentration of Ca (r = -0.85, p < 0.01). This effect was rapid (i.e., observed within 1 h) and could not be attributed to a decrease in the amount of ALP activity in the cells. Phase distribution studies showed that the effect of low Ca to increase ALP release reflected increases in the release of both hydrophilic ALP (i.e., anchorless ALP, released by phosphatidylinositol-glycanase activity) and hydrophobic ALP (i.e., phosphatidylinositol-glycan-anchored ALP, released by membrane vesicle formation). The range of Ca-dependent changes in ALP-specific activity was much smaller than the range of P(i)-dependent changes. The observed correlation between skeletal ALP-specific activity and P(i) was not unique to osteosarcoma cells or to P(i). Similar effects were seen in normal human bone cells in response to P(i) (r = 0.99, p < 0.001) and in SaOS-2 cells in response to a variety of P(i) esters and analogs (e.g., beta-glycero-P(i) and molybdate). Further studies indicated that the effects of phosphoryl compounds on ALP-specific activity could not be correlated with effects on ALP reaction kinetics, cell proliferation, or acid phosphatase activity and that the beta-glycero-P(i)-dependent increase in ALP activity was blocked by cycloheximide but not actinomycin D. Together these data suggest that the function of skeletal ALP may be regulated by P(i) and that Ca may be involved in ALP release.

Alkaline Phosphatase↗
PubMed1992

Nucleoside cyclic 3',5'-phosphates: chair-twist equilibria of the phosphate rings of methyl phosphate and phenylphosphonate derivatives of cTMP.

The cis and trans forms of thymidine methyl cyclic 3',5'-phosphate (9) and of the corresponding phenylphosphonate derivatives (10) were prepared in two steps from the corresponding cyclic amide. 1H NMR spectroscopy showed the phosphorus-containing six-membered rings of cis-9 (MeO and thymin-1-yl cis) to be in the chair conformation, but trans-9 to be approximately 40% in the twist conformation in pyridine-d6 and 33% in acetone-d6. For trans-9, there was resistance of conversion of the chair form into the twist form with the MeO group pseudo-axial with a delta G degrees(C-->T) value of 3.0 kcal/mol. Similarly, for cis-10 (23-39% twist population in CD3CN, acetone-d6, and CDCl3), a delta G degrees(C-->T) value of 0.5-0.6 kcal/mol for placement of the phosphoryl oxygen pseudo-axial was obtained. Both values are taken to be approximations for delta G degrees(C-->T) for cTMP. For trans-10, the twist conformation was populated to the extent of 6-13% with a delta G degrees(C-->T) value of 1.3 kcal/mol.

Hot Temperature↗
PubMed1980

Inhibition of orotidine-5'-phosphate decarboxylase by 1-(5'-phospho-beta-d-ribofuranosyl)barbituric acid, 6-azauridine 5'-phosphate, and uridine 5'-phosphate.

1-(5'-Phospho-beta-D-ribofuranosyl)barbituric acid, an analogue of orotidylic acid, binds to orotidine-5'-phosphate decarboxylase about 100000 times as strongly as does the substrate. The Ki at pH 6 is 9 X 10(-12) M and the half-time for dissociation at 4 degrees C is about 10 h. The binding of the barbiturate analogue to the enzyme is thus one of the strongest interactions between small molecules and proteins that have been measured. The possibility that the inhibitor is a transition-state analogue is discussed.

Carboxy-Lyases↗
PubMed2004

Phosphate transport in Arabidopsis: Pht1;1 and Pht1;4 play a major role in phosphate acquisition from both low- and high-phosphate environments.

Of the mineral nutrients essential for plant growth, phosphorus plays the widest diversity of roles and a lack of phosphorus has profound effects on cellular metabolism. At least eight members of the Arabidopsis Pht1 phosphate (Pi) transporter family are expressed in roots and Pht1;1 and Pht1;4 show the highest transcript levels. The spatial and temporal expression patterns of these two genes show extensive overlap. To elucidate the in planta roles of Pht1;1 and Pht1;4, we identified loss-of-function mutants and also created a double mutant, lacking both Pht1;1 and Pht1;4. Consistent with their spatial expression patterns, membrane location and designation as high-affinity Pi transporters, Pht1;1 and Pht1;4 contribute to Pi transport in roots during growth under low-Pi conditions. In addition, during growth under high-Pi conditions, the double mutant shows a 75% reduction in Pi uptake capacity relative to wildtype. Thus, Pht1;1 and Pht1;4 play significant roles in Pi acquisition from both low- and high-Pi environments.

Arabidopsis↗
PubMed1995

Deprivation of phosphate increases IGF-II mRNA in MDCK cells but IGFs are not involved in phosphate transport adaptation to phosphate deprivation.

Phosphate (Pi) deprivation and IGFs stimulate renal Pi reabsorption. We studied the involvement of IGFs in the adaptation of Pi transport to Pi deprivation in MDCK cells. Deprivation of Pi for 15 h increased the steady-state content of IGF-II mRNA (77 +/- 12%) whereas IGF-I mRNA was not detectable in MDCK cells in either control or Pi-deprived cells. IGF-II (10(-7) M) and IGF-I (10(-8) M) stimulated the Na-dependent Pi uptake (1.23- and 1.3-fold increase at 15 h respectively). The effect of IGF-I appeared after 15 h and increased up to 40 h of treatment (2.15-fold increase). In contrast, Pi uptake was increased by Pi deprivation as early as 8 h (1.5-fold) and up to 40 h of Pi deprivation (1.9-fold increase). IGF-II mRNA was not increased before 15 h of Pi deprivation and returned to control at 40 h. The combination of IGF-I and Pi deprivation had a more than additive effect on Pi transport (fivefold increase) (P < 0.001). At variance with Pi deprivation, high concentrations of insulin stimulated Na-coupled alanine transport (6 +/- 2% and 16 +/- 4% in Pi-treated and Pi-depleted cells respectively). Pi deprivation and high concentrations of insulin decreased Na,K-ATPase activity (-48 and -64% respectively) and these effects were not additive.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Circadian changes in plasma phosphate concentration, urinary phosphate excretion, and cellular phosphate shifts.

The concentration of phosphate (Pi) in plasma, Pi excretion, and the tubular threshold of Pi resorption (TmP/GFR) all increase throughout the day from about 1100 to 0300 h. For plasma [Pi], cosinor analysis yielded the following estimates of the parameters of this pattern (with 95% confidence limits): amplitude = 0.17 (0.07-0.26) mmol/L, phase = peak at 0201 (1127-0342) h, and MESOR = 1.14 (1.11-1.18) mmol/L. The increase in TmP/GFR reflects an underlying change in renal Pi handling, which is not attributable to changes in parathyrin concentrations. The changes in Pi excretion work both for and against the changes in plasma [Pi], at different times. The calculated net nonrenal flux of Pi into the extracellular fluid increases in the morning and remains high until 0300 h, and neither it nor Pi excretion nor plasma [Pi] shows any relation to meals. This illustrates the importance of transient net fluxes of Pi between intracellular and extracellular spaces in the control of hour-to-hour changes of plasma [Pi].

Adult↗
PubMed1983

Phosphate-solubilizing potentiality of the microorganisms capable of utilizing aluminium phosphate as a sole phosphate source.

Eight bacteria, each of the genus Bacillus, two actinomycetes, each of the genus Streptomyces, and six fungi, one each of the genus Penicillium and Chaetomium and four of the genus Aspergillus, were isolated on AlPO4-sucrose agar from a typical Indian lateritic soil (Typic Ochragualf). All of them were capable of solubilizing Ca3(PO4)2 to a higher degree than AlPO4. Bacillus subtilis (B-7655), LAB4, Bacillus sp., LAB5, Penicillium sp., LAF2, and Aspergillus spp., LAF3 and LAF4, were solubilizing Ca3(PO4)2 very efficiently, but AlPO4 to a lesser degree. Bacillus spp., LAB1, LAB2, LAB5, LAB6 and LAB7, Chaetomium nigricolor, LAF1, and Aspergillus spp., LAF5 and LAF6, were unable to bring detectable amounts of soluble phosphorus to solution from AlPO4. Except Chaetomium, all the other organisms produced free aliphatic organic acid in detectable amounts. The organic acids produced were oxalic, succinic, citric, and 2-keto gluconic acid. 2-Keto gluconic acid, singly and in combination with succinic or citric acid, accounted for higher solubilization. Amount of free organic acids in the growth medium was not directly correlated with phosphate solubilization.

Aluminum Compounds↗
PubMed1984

Characterization of phosphate:hexose 6-phosphate antiport in membrane vesicles of Streptococcus lactis.

Membrane vesicles of Streptococcus lactis were used to characterize a novel anion exchange involving phosphate and sugar 6-phosphates. For vesicles loaded with 50 mM phosphate at pH 7, homologous phosphate:phosphate exchange had a maximal rate of 130 nmol/min/mg of protein and a Kt of 0.21 mM external phosphate; among phosphate analogues tested, only arsenate replaced phosphate. Heterologous exchange was studied by 2-deoxyglucose 6-phosphate entry into phosphate-loaded vesicles; this reaction had a maximal velocity of 31 nmol/min/mg of protein and a Kt of 26 microM external substrate. Sugar phosphate moved intact during this exchange, since its entry led to loss of internal 32Pi without transfer of 32P to sugar phosphate. Inhibitions of phosphate exchange suggested that the preferred sugar phosphate substrates were (Kiapp): glucose, 2-deoxyglucose, and mannose 6-phosphates (approximately 20 microM) greater than fructose 6-phosphate (150 microM) greater than glucosamine 6-phosphate (420 microM) greater than alpha-methylglucoside 6-phosphate (740 microM). Stoichiometry for phosphate:2-deoxyglucose 6-phosphate antiport was 2:1 at pH 7, and since initial rates of exchange were unaffected by charge carrying ionophores (gramicidin, valinomycin, a protonophore), this unequal stoichiometry indicated the electroneutral exchange of two monovalent phosphates for a single divalent sugar phosphate.

Binding, Competitive↗
PubMed1985

Effects of intraluminal pH and dietary phosphate on phosphate transport in the proximal convoluted tubule.

The proximal tubule cell adjusts its phosphate absorption appropriately to meet the needs of the organism. Studies were performed to characterize some of the cellular changes involved with dietary phosphate adaptation. First, early proximal convoluted tubules were perfused with equilibrium Ringer solutions buffered to pH 7.65 or 6.5. Saturation kinetics for phosphate transport were determined at each pH value. Rats maintained on a diet of normal phosphate composition demonstrated the apparent Jmax and Km parameters about twofold greater with intraluminal pH 7.65 vs. pH 6.5. The Jmax values increased to 53.47 +/- 3.71 and 42.73 +/- 5.48 pmol X min-1 X mm-1, respectively, when the rats were placed on a phosphate-restricted diet for 5 days. By contrast, adaptation to a high dietary phosphate content resulted in diminished phosphate absorption, 8.53 +/- 1.80 and 12.87 +/- 1.61 pmol X min-1 X mm-1, for the respective pH 7.65 and 6.5 values. Second, the effect of peritubule phosphate concentration was evaluated at constant intraluminal phosphate concentrations. Unidirectional lumen-to-blood phosphate efflux was inhibited at all plasma phosphate concentrations in animals maintained on normal dietary phosphate. By contrast, rats adapted to a low phosphate diet exhibited an increase in phosphate absorption: pH 7.65, 86.21 +/- 2.63, and pH 6.5, 140.84 +/- 86.76 pmol X min-1 X mm-1 when plasma concentrations were elevated two- or three-fold from 2.4 to 6.4 mM. This was attributed to enhanced phosphate exchange on the basolateral membrane. Further hyperphosphatemic levels, above 6.4 mM, inhibited phosphate absorption. These data suggest that net phosphate absorption is determined, in part, by factors other than sodium-dependent uptake of phosphate by the brush border membrane including intracellular pH and peritubular phosphate that act in concert to control renal phosphate absorption.

Absorption↗
PubMed2005

Ribose-5-phosphate biosynthesis in Methanocaldococcus jannaschii occurs in the absence of a pentose-phosphate pathway.

Recent work has raised a question as to the involvement of erythrose-4-phosphate, a product of the pentose phosphate pathway, in the metabolism of the methanogenic archaea (R. H. White, Biochemistry 43:7618-7627, 2004). To address the possible absence of erythrose-4-phosphate in Methanocaldococcus jannaschii, we have assayed cell extracts of this methanogen for the presence of this and other intermediates in the pentose phosphate pathway and have determined and compared the labeling patterns of sugar phosphates derived metabolically from [6,6-2H2]- and [U-13C]-labeled glucose-6-phosphate incubated with cell extracts. The results of this work have established the absence of pentose phosphate pathway intermediates erythrose-4-phosphate, xylose-5-phosphate, and sedoheptulose-7-phosphate in these cells and the presence of D-arabino-3-hexulose-6-phosphate, an intermediate in the ribulose monophosphate pathway. The labeling of the D-ara-bino-3-hexulose-6-phosphate, as well as the other sugar-Ps, indicates that this hexose-6-phosphate was the precursor to ribulose-5-phosphate that in turn was converted into ribose-5-phosphate by ribose-5-phosphate isomerase. Additional work has demonstrated that ribulose-5-phosphate is derived by the loss of formaldehyde from D-arabino-3-hexulose-6-phosphate, catalyzed by the protein product of the MJ1447 gene.

Aldose-Ketose Isomerases↗
PubMed2001

Stimulation of intracellular sphingosine-1-phosphate production by G-protein-coupled sphingosine-1-phosphate receptors.

Recently, a family of G-protein-coupled receptors named endothelial differentiation gene (Edg) receptor family has been identified, which are specifically activated by the two serum lipids, sphingosine-1-phosphate and lysophosphatidic acid. Sphingosine-1-phosphate can also act intracellularly to release Ca2+ from intracellular stores. Since in several cell types, G-protein-coupled lysophosphatidic acid or sphingosine-1-phosphate receptors mobilize Ca2+ in the absence of a measurable phospholipase C stimulation, it was analysed here whether intracellular sphingosine-1-phosphate production was the signalling mechanism used by extracellular sphingosine-1-phosphate for mobilization of stored Ca2+. Sphingosine-1-phosphate and the low affinity sphingosine-1-phosphate receptor agonist, sphingosylphosphorylcholine, induced a rapid, transient and nearly complete pertussis toxin-sensitive Ca2+ mobilization in human embryonic kidney (HEK-293) cells. The G-protein-coupled sphingosine-1-phosphate receptors, Edg-1, Edg-3 and Edg-5, were found to be endogenously expressed in these cells. Most interestingly, sphingosine-1-phosphate and sphingosylphosphorylcholine did not induce a measurable production of inositol-1,4,5-trisphosphate or accumulation of inositol phosphates. Instead, sphingosine-1-phosphate and sphingosylphosphorylcholine induced a rapid and transient increase in production of intracellular sphingosine-1-phosphate with a maximum of about 1.4-fold at 30 s. Stimulation of sphingosine-1-phosphate formation by sphingosine-1-phosphate and sphingosylphosphorylcholine was fully blocked by pertussis toxin, indicating that extracellular sphingosine-1-phosphate via endogenously expressed G(i)-coupled receptors induces a stimulation of intracellular sphingosine-1-phosphate production. As sphingosine-1-phosphate- and sphingosylphosphorylcholine-induced increases in intracellular Ca2+ were blunted by sphingosine kinase inhibitors, this sphingosine-1-phosphate production appears to mediate Ca2+ signalling by extracellular sphingosine-1-phosphate and sphingosylphosphorylcholine in HEK-293 cells.

Calcium Signaling↗
PubMed1989

P-Nuclear Magnetic Resonance Determination of Phosphate Compartmentation in Leaves of Reproductive Soybeans (Glycine max L.) as Affected by Phosphate Nutrition.

Most leaf phosphorus is remobilized to the seed during reproductive development in soybean. We determined, using (31)P-NMR, the effect phosphorus remobilization has on vacuolar inorganic phosphate pool size in soybean (Glycine max [L.] Merr.) leaves with respect to phosphorus nutrition and plant development. Phosphate compartmentation between cytoplasmic and vacuolar pools was observed and followed in intact tissue grown hydroponically, at the R2, R4, and R6 growth stages. As phosphorus in the nutrient solution decreased from 0.45 to 0.05 millimolar, the vacuolar phosphate peak became less prominent relative to cytoplasmic phosphate and hexose monophosphate peaks. At a nutrient phosphate concentration of 0.05 millimolar, the vacuolar phosphate peak was not detectable. At higher levels of nutrient phosphate, as plants progressed from the R2 to the R6 growth stage, the vacuolar phosphate peak was the first to disappear, suggesting that storage phosphate was remobilized to a greater extent than metabolic phosphate. Under suboptimal phosphate nutrition (</= 0.20 millimolar), the hexose monophosphate and cytoplasmic phosphate peaks declined earlier in reproductive development than when phosphate was present in optimal amounts. Under low phosphate concentrations (0.05 millimolar) cytoplasmic phosphate was greatly reduced. Carbon metabolism was coincidently disrupted under low phosphate nutrition as shown by the appearance of large, prominent starch grains in the leaves. Cytoplasmic phosphate, and leaf carbon metabolism dependent on it, are buffered by vacuolar phosphate until late stages of reproductive growth.

Journal Article↗
PubMed1975

The relative utilization of the acyl dihydroxyacetone phosphate and glycerol phosphate pathways for synthesis of glycerolipids in various tumors and normal tissues.

Rates of phosphatidate synthesis from dihydroxyacetone phosphate via acyl dihydroxyacetone phosphate or glycerol phosphate are compared in homogenates of 13 tissues, most of which are deficient in glycerol phosphate dehydrogenase (EC 1.1.1.8). In all tissues examined, dihydroxyacetone phosphate entered phosphatidate more rapidly via acyl dihydroxyacetone phosphate than via glycerol phosphate. Tissues with a relatively low rate of phosphatidate synthesis via glycerol phosphate, showed no compensating increase in the rate of synthesis via acyl dihydroxyacetone phosphate. The rates at which tissue homogenates synthesize phosphatidate from dihydroxyacetone phosphate via glycerol phosphate increase as glycerol phosphate dehydrongenase increase. Both glycerol phosphate dehydrogenase and glycerol phosphate: acyl CoA acyltransferase (EC 2.3.1.15) are more active than dihydroxyacetone phosphate : acyl CoA acyltransferase (EC 2.3.1.42). Thus, all the tissue homogenates possessed an apparently greater capability to synthesize phosphatidate via glycerol phosphate than via acyl dihydroxyacetone phosphate, but did not express this potential. This result is discussed in relation to in vivo substrate limitations.

Acyltransferases↗
PubMed2002

The plastidic pentose phosphate translocator represents a link between the cytosolic and the plastidic pentose phosphate pathways in plants.

Plastids are the site of the reductive and the oxidative pentose phosphate pathways, which both generate pentose phosphates as intermediates. A plastidic transporter from Arabidopsis has been identified that is able to transport, in exchange with inorganic phosphate or triose phosphates, xylulose 5-phosphate (Xul-5-P) and, to a lesser extent, also ribulose 5-phosphate, but does not accept ribose 5-phosphate or hexose phosphates as substrates. Under physiological conditions, Xul-5-P would be the preferred substrate. Therefore, the translocator was named Xul-5-P/phosphate translocator (XPT). The XPT shares only approximately 35% to 40% sequence identity with members of both the triose phosphate translocator and the phosphoenolpyruvate/phosphate translocator classes, but a higher identity of approximately 50% to glucose 6-phosphate/phosphate translocators. Therefore, it represents a fourth group of plastidic phosphate translocators. Database analysis revealed that plant cells contain, in addition to enzymes of the oxidative branch of the oxidative pentose phosphate pathway, ribose 5-phosphate isomerase and ribulose 5-phosphate epimerase in both the cytosol and the plastids, whereas the transketolase and transaldolase converting the produced pentose phosphates to triose phosphates and hexose phosphates are probably solely confined to plastids. It is assumed that the XPT function is to provide the plastidic pentose phosphate pathways with cytosolic carbon skeletons in the form of Xul-5-P, especially under conditions of a high demand for intermediates of the cycles.

Aldose-Ketose Isomerases↗