Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PENTOSES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,603 records · Page 89Linked to original sources
PubMed1967

Photosynthesis in Rhodospirillum rubrum. II. Photoheterotrophic carbon dioxide fixation.

The contribution of the reductive pentose phosphate cycle to the photometabolism of carbon dioxide and to carbon metabolism in Rhodospirillum rubrum grown photoheterotrophically with l-malate as the carbon source is nil, unlike autotrophically grown R. rubrum. Glycolic acid appears to be the first stable product of CO(2) fixation in R. rubrum cultured photoheterotrophically on l-malate. The results obtained in (14)CO(2) fixation experiments suggest that the photometabolism of CO(2) through glycolate into malate is a major pathway of CO(2) fixation in such cells. However, l-malate was a much more efficient precursor of phosphate esters, and of glutamic acid, than was carbon dioxide; l-malate is therefore, in this case, a far more important source of cell carbon than is carbon dioxide. The products of the light-dependent incorporation of CO(2) and of acetate were investigated in R. rubrum grown photoheterotrophically on acetate. Carboxylation reactions and the reductive pentose phosphate cycle are apparently of greater significance in the photometabolism of acetate heterotrophs than in malate heterotrophs; the photometabolism of the acetate photoheterotrophs seems to be intermediate between the photoheterotrophy of malate heterotrophs and strict autotrophy.

Carbon↗
PubMed1967

Respiratory metabolism in buckwheat seedlings.

Young seedlings of buckwheat (Fagopyrum esculentum) respire in air with an RQ of unity. Analysis of respiratory substrates coupled with a study of the utilization of acetate-(14)C and glucose-(14)C suggest that both the Embden-Meyerhof-Parnas, tricarboxylic acid and pentose phosphate sequences participate in the total respiratory catabolism.In anoxia CO(2) dropped to one third of the aerobic rate and ethanol accumulated to only about one half the rate of CO(2) output on a molar basis. Smaller amounts of lactate, succinate and free amino acids (particularly alanine and gamma-aminobutyric acid) accumulated, carboxylic acids decreased and there were initial increased in pyruvate and alpha-ketoglutarate. The observed changes are consistent with residual tricarboxylic acid and pentose phosphate cycle activity in anoxia and may account for the excess CO(2) production over ethanol accumulation. CO(2), ethanol and lactate production did not account for all of the carbohydrate consumed in anoxia.Relative rates of carbon loss were measured in air and in atmospheres containing 3.5%, 2.1%, 1.3% and 0.6% oxygen. The extinction point of anaerobic metabolism was 1.5%.On return to air from anoxia the CO(2) output increased and the RQ rose from 0.8 to 1.0 over the first 2-hour period. Ethanol, lactate and succinate were consumed and other constituents returned to their previous aerobic level. Some of these changes suggest a rather slow resumption of tricarboxylic acid cycle activity on return to air.Carbon loss as CO(2) in air was greater than the carbon loss as CO(2) at the extinction point. Carbon loss in anoxia as CO(2), ethanol and lactate was similar to carbon loss at the extinction point. Assessed in this orthodox manner buckwheat seedlings show no Pasteur effect but the complex nature of the changes in levels of metabolic substrates and intermediates do not allow firm conclusions to be drawn on the effects of oxygen on the rates of glycolysis and other respiratory processes.

Journal Article↗
PubMed1971

Photosynthetic CO(2) Fixation Products and Activities of Enzymes Related to Photosynthesis in Bermudagrass and Other Plants.

After a 5-second exposure of illuminated bermudagrass (Cynodon dactylon L. var. ;Coastal') leaves to (14)CO(2), 84% of the incorporated (14)C was recovered as aspartate and malate. After transfer from (14)CO(2)-air to (12)CO(2)-air under continuous illumination, total radioactivity decreased in aspartate, increased in 3-phosphoglyceric acid and alanine, and remained relatively constant in malate. Carbon atom 1 of alanine was labeled predominantly, which was interpreted to indicate that alanine was derived from 3-phosphoglyceric acid. The activity of phosphoenolpyruvate carboxylase, alkaline pyrophosphatase, adenylate kinase, pyruvate-phosphate dikinase, and malic enzyme in bermudagrass leaf extracts was distinctly higher than those in fescue (Festuca arundinacea Schreb.), a reductive pentose phosphate cycle plant. Assays of malic enzyme activity indicated that the decarboxylation of malate was favored. Both malic enzyme and NADP(+)-specific malic dehydrogenase activity were low in bermudagrass compared to sugarcane (Saccharum officinarum L.). The activities of NAD(+)-specific malic dehydrogenase and acidic pyrophosphatase in leaf extracts were similar among the plant species examined, irrespective of the predominant cycle of photosynthesis. Ribulose-1, 5-diphosphate carboxylase in C(4)-dicarboxylic acid cycle plant leaf extracts was about 60%, on a chlorophyll basis, of that in reductive pentose phosphate cycle plants.We conclude from the enzyme and (14)C-labeling studies that bermudagrass contains the C(4)-dicarboxylic acid cycle and that pyruvate-phosphate dikinase does not exist exclusively in C(4)-dicarboxylic acid cycle plants, and we propose that in C(4)-dicarboxylic acid cycle plants the transfer of carbon from a dicarboxylic acid to 3-phosphoglyceric acid involves a decarboxylation reaction and then a refixation of carbon dioxide by ribulose-1, 5-diphosphate carboxylase.

Journal Article↗
PubMed1972

High photosynthetic rate of a chlorophyll mutant of cotton.

In a chlorophyll mutant (virescent) and wild-type cotton (Gossypium hirsutum L.), a number of photosynthetic parameters have been measured and compared with those published for other chlorophyll mutants. (a) The photosynthetic rates at 230 w/m(2) (400-700 nm) from a tungsten lamp were 36.8 mg CO(2) fixed/dm(2).hr (virescent) and 39.5 mg CO(2) fixed/dm(2).hr (wild-type). On a chlorphyll basis, the photosynthetic rates were 36.8 and 12.1 mg CO(2) fixed/mg chl.hr, respectively. (b) The photosynthetic rates at 13 w/m(2) (400-700 nm) from a tungsten source were 7.1 mg CO(2) fixed/dm(2).hr (virescent) and 7.4 mg CO(2) fixed/dm(2).hr (wild-type). On a chlorophyll basis, the photosynthetic rates were 6.0 and 1.4 mg CO(2) fixed/mg chl.hr, respectively. (c) The chlorophyll a/b ratios of the virescent and wild-type leaves were 3.3 and 4.1 (d) The chlorophyll/carotenoid ratios for the virescent and wild-type leaves were 3.2 and 7.3, respectively. (e) The photosynthetic carbon metabolism of the chlorophyll mutant was through the reductive pentose phosphate cycle. (f) The CO(2) compensation points for the virescent and wild-type plants were similar. (g) The mutant and wild-type leaves have the same quantum yield in the red part of the visible spectrum, but the virescent leaves have a lower quantum yield in the blue part of the spectrum. (h) Virescent and wild-type leaves contain similar levels on a protein basis of several reductive pentose phosphate cycle enzymes.

Journal Article↗
PubMed1977

Effect of a myo-Inositol Antagonist, 2-O, C-Methylene-myo-Inositol, on the Metabolism of myo-Inositol-2-H and d-Glucose-1-C in Lilium longiflorum Pollen.

2-O,C-Methylene-myo-inositol (MMO), a myo-inositol (MI) antagonist, inhibits germination and tube elongation of pollen from Lilium longiflorum cv. Ace or 44. The presence of 5 mm MMO in Dickinson's pentaerythritol medium (Plant Physiol. 43:1-8) partially blocks germination. The tubes produced are short and fail to elongate. In the presence of MI, MMO's toxic effect is blocked. As little as 0.56 mm MI will maintain normal germination in the presence of 43 mm MMO, and pollen tubes continue to elongate for 2 to 3 hr. Eventually, the toxic action of MMO prevents further growth. MMO does not inhibit UDP-d-glucose dehydrogenase from lily pollen.Uptake of MI-2-(3)H and incorporation of tritium into galacturonic acid and pentose units of tube wall pectin are blocked by MMO. The site of this inhibition is undertermined. Uptake of d-glucose-1-(14)C and incorporation of (14)C into 70% ethyl alcohol-insoluble polysaccharides of germinated pollen are not blocked by MMO, but distribution of label into polysaccharide product is altered. In MMO-treated pollen, very little (14)C is found in uronic acid or pentose units. At 30 mm MMO, about two-thirds of the carbon flow from d-glucose to these pectic components is interrupted. MMO also alters d-glucose metabolism in the 70% ethyl alcohol-soluble fraction, but the compound involved must still be identified.These results offer fresh evidence of an intermediary role for MI during UDP-d-glucuronate biosynthesis in germinated pollen.

Journal Article↗
PubMed1977

Steady-state photosynthesis in alfalfa leaflets: effects of carbon dioxide concentration.

When the CO(2) concentration to which Medicago sativa L. var. El Unico leaflets were exposed was increased from half-saturation to saturation (doubled rate of photosynthesis), glycolate and glycine production apparently decreased due to inhibition of a portion of the glycolate pathway. Serine and glycerate production was not inhibited. We conclude that serine and glycerate were made from 3-phosphoglycerate and not from glycolate and that the conversion of glycine to serine may not be the major source of photorespiratory CO(2) in alfalfa. In investigations of glycolate and photorespiratory metabolism, separate labeling data should be obtained for glycine and serine as those two amino acids may be produced from different precursors and respond differently to environmental perturbations. The increased photosynthetic rate (at saturating CO(2)) resulted in greater labeling of both soluble and insoluble products. Sucrose labeling increased sharply, but there was no major shift of tracer carbon flow into sucrose relative to other metabolites. The flow of carbon from the reductive pentose phosphate cycle into the production of tricarboxylic acid cycle intermediates and amino acids increased. Only small absolute increases occurred in steady-state pool sizes of metabolites of the reductive pentose phosphate cycle at elevated CO(2), providing further evidence that the cycle is well regulated.

Journal Article↗
PubMed1978

Light modulation of the activity of carbon metabolism enzymes in the crassulacean Acid metabolism plant kalanchoë.

When intact Kalanchoë plants are illuminated NADP-linked malic dehydrogenase and three enzymes of the reductive pentose phosphate pathway, ribulose-5-phosphate kinase, NADP-linked glyceraldehyde-3-phosphate dehydrogenase, and sedoheptulose-1,7-diphosphate phosphatase, are activated. In crude extracts these enzymes are activated by dithiothreitol treatment. Light or dithiothreitol treatment does not inactivate the oxidative pentose phosphate pathway enzyme glucose-6-phosphate dehydrogenase. Likewise, neither light, in vivo, nor dithiothreitol, in vitro, affects fructose-1,6-diphosphate phosphatase. Apparently the potential for modulation of enzyme activity by the reductively activated light effect mediator system exists in Crassulacean acid metabolism plants, but some enzymes which are light-dark-modulated in the pea plant are not in Kalanchoë.

Journal Article↗
PubMed1979

Carbon Dioxide Fixation by Lupin Root Nodules: II. Studies with C-labeled Glucose, the Pathway of Glucose Catabolism, and the Effects of Some Treatments That Inhibit Nitrogen Fixation.

Labeling studies using detached lupin (Lupinus angustifolius) nodules showed that over times of less than 3 minutes, label from [3,4-(14)C]glucose was incorporated into amino acids, predominantly aspartic acid, to a much greater extent than into organic acids. Only a slight preferential incorporation was observed with [1-(14)C]- and [6-(14)C]glucose, while with [U-(14)C]-glucose more label was incorporated into organic acids than into amino acids at all labeling times. These results are consistent with a scheme whereby the "carbon skeletons" for amino acid synthesis are provided by the phosphoenolpyruvate carboxylase reaction.A comparison of (14)CO(2) release from nodules supplied with [1-(14)C]- and [6-(14)C]glucose indicated that the oxidative pentose phosphate pathway accounted for less than 6% of glucose metabolism. Several enzymes of the oxidative pentose phosphate and glycolytic pathways were assayed in vitro using the 12,000g supernatant fraction from nodule homogenates. In all cases, the specific activities were adequate to account for the calculated in vivo fluxes.Three out of four diverse treatments that inhibited nodule nitrogen fixation also inhibited nodule CO(2) fixation, and in the case of the fourth treatment, replacement of N(2) with He, it was shown that the normal entry of label from exogenous (14)CO(2) into the nodule amino acid pool was strongly inhibited.

Journal Article↗
PubMed1979

Orthophosphate control of glucose-6-phosphate dehydrogenase light modulation in relation to the induction phase of chloroplast photosynthesis.

High concentrations of orthophosphate (Pi) inhibited CO(2)-dependent O(2) evolution and prevented the inactivation of glucose-6-P dehydrogenase by light in intact spinach and barley chloroplasts. Addition of glycerate-3-P to chloroplasts inhibited by Pi in the light, induced O(2) evolution and caused rapid inactivation of glucose-6-P dehydrogenase. The activity of phosphofructokinase detected in chloroplast preparations was not affected by light or by Pi.Dihydroxyacetone-P was a major product of chloroplast photosynthesis when optimum concentrations of Pi were used. Chloroplasts continued to form dihydroxyacetone-P at a slow rate in the presence of Pi at concentrations (2 to 4 millimolar) that gave complete inhibition of CO(2)-dependent O(2) evolution. Formation of dihydroxyacetone-P in the presence of 4 millimolar Pi was stimulated by light and either O(2) (150 micromolar) or sparker amounts of oxaloacetate.Conditions that favored dihydroxyacetone-P formation (high O(2) or low O(2) plus oxaloacetate) increased the optimum Pi concentration for CO(2)-dependent O(2) evolution and stimulated O(2) evolution at high concentrations of Pi. The stimulation of O(2) evolution at superoptimal concentrations of Pi by O(2) or oxaloacetate was prevented by dithiothreitol.The results suggested that formation of pentose-P pathway intermediates via the oxidative pentose-P pathway may be limited by availability of NADP in the light but may occur at significant rates and thereby contribute to termination of the induction phase of O(2) evolution.

Journal Article↗
PubMed1982

On the Participation of Phosphoribulokinase in the Light Regulation of CO(2) Fixation.

CO(2) fixation by a suspension of isolated spinach chloroplasts was terminated by turning off the light, and changes of metabolite levels in the chloroplast stroma and the surrounding medium were assayed. Whereas CO(2) fixation comes to a total stop within 15 seconds, a conversion of triose phosphates to heptose, hexose, and pentose monophosphates is found to occur for 1 to 2 minutes afterwards. It seems from these data that an inactivation of fructose and sedoheptulose bisphosphatases proceeds with a lag period. In contrast, the conversion of pentose monophosphates to ribulose 1,5-bisphosphate is inhibited immediately after the stop of illumination. As the stromal level of freely available ATP was not depleted under this condition, these data demonstrate that ribulose 5-phosphate kinase was very rapidly inactivated after darkening of the chloroplasts. Essentially, the same effect is also observed when CO(2) fixation is partially inhibited by addition of moderate concentrations of m-chlorocarbonyl phenylhydrazone, partially uncoupling photophosphorylation. It appears from these results, that the activity of ribulose 5-phosphate kinase is not only regulated by light through the mediation of reduced carriers like thioredoxin but also by alternative parameters, e.g. stromal metabolite levels.

Journal Article↗
PubMed1983

Metabolism of C-labeled photosynthate and distribution of enzymes of glucose metabolism in soybean nodules.

The metabolism of translocated photosynthate by soybean (Glycine max L. Merr.) nodules was investigated by (14)CO(2)-labeling studies and analysis of nodule enzymes. Plants were exposed to (14)CO(2) for 30 minutes, followed by (12)CO(2) for up to 5 hours. The largest amount of radioactivity in nodules was recovered in neutral sugars at all sampling times. The organic acid fraction of the cytosol was labeled rapidly. Although cyclitols and malonate were found in high concentrations in the nodules, they accumulated less than 10% of the radioactivity in the neutral and acidic fractions, respectively. Phosphate esters were found to contain very low levels of total label, which prohibited analysis of the radioactivity in individual compounds. The whole nodule-labeling patterns suggested the utilization of photosynthate for the generation of organic acids (principally malate) and amino acids (principally glutamate).The radioactivity in bacteroids as a percentage of total nodule label increased slightly with time, while the percentage in the cytosol fraction declined. The labeling patterns for the cytosol were essentially the same as whole nodule-labeling patterns, and they suggest a degradation of carbohydrates for the production of organic acids and amino acids. When it was found that most of the radioactivity in bacteroids was in sugars, the enzymes of glucose metabolism were surveyed. Bacteroids from nodules formed by Rhizobium japonicum strain 110 or strain 138 lacked activity for phosphofructokinase and NADP-dependent 6-phosphogluconate dehydrogenase, key enzymes of glycolysis and the oxidative pentose-phosphate pathways. Enzymes of the glycolytic and pentose phosphate pathways were found in the cytosol fraction.In three experiments, bacteroids contained about 10 to 30% of the total radioactivity in nodules 2 to 5 hours after pulse-labeling of plants, and 60 to 65% of the radioactivity in bacteroids was in the neutral sugar fraction at all sampling times. This strongly suggests some absorption and metabolism of sugars by bacteroids in spite of the lack of key enzymes. Bacteroids did possess enzymes for the formation of hexose phosphates from glucose or fructose. Radioactivity in alpha,alpha-trehalose in bacteroids increased until, after 5 hours, trehalose was a major labeled compound in bacteroids. Thus, trehalose synthesis may be a major fate of sugars entering bacteroids.

Journal Article↗
PubMed1985

Effect of Water Stress on the Carbohydrate Metabolism of Citrullus lanatus Seeds during Germination.

Gluconeogenesis in Citrullus lanatus seeds is a post germinative event. Increases in isocitrate lyase activity and incorporation of radioactivity from [2-(14)C]acetate into sugars occur only after radicle emergence. During germination, the seeds appear to rely on carbohydrate as the respiratory substrate. At this time, glycolysis, the pentose phosphate pathway, and the tricarbocyclic acid cycle seem to be functional. Utilization of raffinose during germination appears to be important.Water stress, which completely inhibits germination, has a marked effect on carbohydrate metabolism. The rate of (14)CO(2) release from [2-(14)C]acetate, [1-(14)C]glucose, and [6-(14)C]glucose is lower in the stressed seeds than the control seeds during the respiratory lag phase. However, in the stressed seeds neither glycolysis, the pentose phosphate pathway, nor the tricarboxylic acid cycle is completely inhibited. In contrast to the control seeds in which raffinose content sharply declines after 12 h of incubation, raffinose content in the stressed seeds remains fairly constant.The respiratory lag phase of the control seeds coincides with a lower reducing substance content, glucose content, and fructose content than in the stressed seeds during the corresponding incubation period.

Journal Article↗
PubMed1986

myo-Inositol Synthesis from [1-H]Glucose in Phaseolus vulgaris L. during Early Stages of Germination.

Radiolabeled d-[1-(3)H]glucose was fed by imbibition under sterile conditions to bean (Phaseolus vulgaris L.) seeds. After 72 and 96 hours of feeding, the (3)H was located in uronic acid and pentose residues as well as hexose residues of cell wall polysaccharides in growing hypocotyl and root. Free myo-inositol present in cotyledons, hypocotyl, and root also contained (3)H, showing that de novo synthesis of myo-inositol from [1-(3)H]glucose did occur during the first 72 hours of germination. More than 90% of the labeled, free myo-inositol was present in the cotyledons. The (3)H percentage in trifluoroacetic acid-soluble arabinose residues of cell wall polysaccharides from 72-hour-old bean hypocotyls was only half of their mole percentage. On the other hand, (3)H percentages in hexose residues were higher than their mole percentages. The results suggest that myo-inositol is synthesized from reserve sugars during the very early stages of germination, and that the newly synthesized myo-inositol, as well as that stored in cotyledons, can be used for the construction of new hypocotyl and root cell wall polysaccharides after conversion into uronic acids and pentoses via the myo-inositol oxidation pathway.

Journal Article↗
PubMed1989

Inhibition of chloroplastic respiration by osmotic dehydration.

The respiratory capacity of isolated spinach (Spinacia oleracea L.) chloroplasts, measured as the rate of (14)CO(2) evolved from the oxidative pentose phosphate cycle in darkened chloroplasts exogenously supplied with [(14)C]glucose, was progressively diminished by escalating osmotic dehydration with betaine or sorbitol. Comparing the inhibitions of CO(2) evolution generated by osmotic dehydration in chloroplasts given C-1 and C-6 labeled glucose, 54% and 84% respectively, indicates that osmotic dehydration effects to a greater extent the recycling of the oxidative pentose phosphate intermediates, fructose-6P and glyceraldehyde-3P. Respiratory inhibition in the darkened chloroplast could be alleviated by addition of NH(4)Cl (a stromal alkylating agent), iodoacetamide) an inhibitor of glyceraldehyde-3P dehydrogenase), or glycolate-2P (an inhibitor of phosphofructokinase). It is concluded that the site which primarily mediates respiratory inhibition in the darkened chloroplast occurs at the fructose 1,6-bisphosphatase/phosphofructokinase junction.

Journal Article↗
PubMed1990

Effect of Boron Deficiency on Photosynthesis and Reductant Sources and Their Relationship with Nitrogenase Activity in Anabaena PCC 7119.

Nitrogenase activity of Anabaena PCC 7119 is inhibited under conditions of boron deficiency. To elucidate the mechanisms of this inhibition, this study examined how the deficiency of boron affected photosynthesis, photosynthetic pigments, the enzymes of the oxidative pentose phosphate pathway, and respiration of Anabaena PCC 7119 cultures. After 24 to 48 hours of boron deficiency, reductions in photosynthetic O(2) evolution and in CO(2) fixation were observed. At the same time, the activities of oxidative pentose phosphate pathway enzymes and respiration increased significantly with boron deficiency. No change was observed in these processes when assays were performed after 4 to 6 hours of deficiency, a time at which nitrogenase activity was severely inhibited. These results suggest that the requirement for boron in N(2) fixation is independent of its effects on photosynthesis and reductant supply.

Journal Article↗
PubMed1991

Glucose Respiration in the Intact Chloroplast of Chlamydomonas reinhardtii.

Chloroplastic respiration was monitored by measuring (14)CO(2) from (14)C glucose in the darkened Chlamydomonas reinhardtii F-60 chloroplast. The patterns of (14)CO(2) evolution from labeled glucose in the absence and presence of the inhibitors iodoacetamide, glycolate-2-phosphate, and phosphoenolpyruvate were those expected from the oxidative pentose phosphate cycle and glycolysis. The K(m) for glucose was 56 micromolar and for MgATP was 200 micromolar. Release of (14)CO(2) was inhibited by phloretin and inorganic phosphate. Comparing the inhibition of CO(2) evolution generated by pH 7.5 with respect to pH 8.2 (optimum) in chloroplasts given C-1, C-2, and C-6 labeled glucose indicated that a suboptimum pH affects the recycling of the pentose phosphate intermediates to a greater extent than CO(2) evolution from C-1 of glucose. Respiratory inhibition by pH 7.5 in the darkened chloroplast was alleviated by NH(4)Cl and KCl (stromal alkalating agents), iodoacetamide (an inhibitor of glyceraldehyde 3-phosphate dehydrogenase), or phosphoenolpyruvate (an inhibitor of phosphofructokinase). It is concluded that the site which primarily mediates respiration in the darkened Chlamydomonas chloroplast is the fructose-1,6-bisphosphatase/phosphofructokinase junction. The respiratory pathways described here can account for the total oxidation of a hexose to CO(2) and for interactions between carbohydrate metabolism and the oxyhydrogen reaction in algal cells adapted to a hydrogen metabolism.

Journal Article↗
PubMed1991

Regulation of glycerol synthesis in response to osmotic changes in dunaliella.

Changes in phosphometabolites, following osmotic shock, were analyzed by two-dimensional thin layer chromatography, in extracts of the halotolerant alga Dunaliella salina in order to clarify the regulation of glycerol synthesis from starch. The experiments were carried out in wild-type and in osmotically defective mutant cells. It is demonstrated that hyperosmotic shock induces a decrease in fructose 6-phosphate and an increase in fructose-1,6-bisphosphate indicating the activation of phosphofructokinase. Two mutants, which are specifically defective in their response to hyperosmotic shock, accumulate glucose 6-phosphate or phosphogluconate following shock, and have remarkably reduced activities of glucose-6-phosphate dehydrogenase and of phosphogluconate dehydrogenase, respectively. These results indicate that the pentose-phosphate oxidative pathway has a major role in glycerol synthesis. Hyperosmotic shock leads to a transient accumulation of phosphorylcholine and to a decrease of inositolbisphosphate in D. salina extracts. Accumulation of phosphorylcholine is not detected in osmotically defective mutants. Hypoosmotic shock induces an increase in inositolbisphosphate but not in phosphorylcholine. These results are consistent with previous indications for differential activations of phospholipases by hyper or hypoosmotic shock in Dunaliella. Based on these results we suggest that (a) phosphofructokinase is an important checkpoint enzyme in the regulation of glycerol production, and (b) that the pentose-phosphate pathway has a major role in keeping oxidation-reduction balance during glycerol synthesis. The possible role of lipid breakdown products as second messengers in regulating glycerol production in Dunaliella is discussed.

Journal Article↗
PubMed1992

Specific reduction of wheat storage proteins by thioredoxin h.

Gliadins and glutenins, the major storage proteins of wheat endosperm (Triticum durum, Desf. cv Monroe), were reduced in vitro by the NADP/thioredoxin system (NADPH, NADP-thioredoxin reductase and thioredoxin; in plants, the h type) from either the same source or the bacterium Escherichia coli. A more limited reduction of certain members of these protein groups was achieved with the reduced form of glutathione or glutaredoxin, a protein known to replace thioredoxin in certain bacterial and mammalian enzyme systems but not known to occur in higher plants. Endosperm extracts contained the enzymes necessary to reduce NADP by the oxidative pentose phosphate pathway (hexokinase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase). The gliadins and glutenins were also reduced in vivo during germination--an event that accompanied their proteolytic breakdown. The results suggest that thioredoxin, reduced by NADPH generated via the oxidative pentose phosphate pathway, functions as a signal in germination to enhance metabolic processes such as the mobilization of storage proteins and, as found earlier, the activation of enzymes.

Germination↗