Suppressor of Phosphofructokinase Mutations of Escherichia coli

The known locus of fructose-6-phosphate kinase mutations (pfkA) in Escherichia coli is at 76 min on the genetic map. We have now found another gene, pfkB, at 33 min, mutation of which suppresses pfkA mutations. The suppression is not informational, and pfkB may be a second gene for fructose-6-phosphate kinase activity.     

Changes of pentose phosphate pathway flux in vivo in Corynebacterium glutamicum during leucine-limited batch cultivation as determined from intracellular metabolite concentration measurements

Corynebacterium glutamicum is an important organism for the industrial production of amino acids such as lysine. In the present study time-dependent changes in the oxidative pentose phosphate pathway activity, an important site of NADPH regeneration in C. glutamicum, are investigated, whereby intracellular metabolite concentrations and specific enzyme activities in two isogenic leucine auxotrophic strains differing only in the regulation of their aspartate kinases were compared. After leucine limitation only the strain with a feedback-resistant aspartate kinase began to excrete lysine into the culture medium. Concomitantly, the intracellular NADPH to NADP concentration ratio increased from 2 to 4 in the non-producing strain, whereas it remained constant at about 1.2 in the lysine-producing strain. From these data the in'vivo flux through the pentose phosphate pathway was calculated. These results were used to approximate the total NADPH regeneration by glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and isocitrate dehydrogenase, which agreed fairly well with the calculated demands for biomass formation and lysine biosynthesis. The analysis allowed to conclude that NADPH regeneration in the pentose phosphate pathway is essential for lysine biosynthesis in C. glutamicum.     

Construction of a constitutively expressed homo-fermentative pathway in Lactobacillus brevis

Lactobacillus brevis is a promising lactic acid producing strain that simultaneously utilizes glucose and xylose from lignocellulosic hydrolysate without carbon catabolic repression and inhibition. The production of by-products acetic acid and ethanol has been the major drawback of this strain. Two genes, pfkA (fructose-6-phosphate kinase [PFK]) and fbaA (fructose-1,6-biphosphate aldolase [FBA]), that encode the key enzymes of the EMP/glycolytic pathway from Lactobacillus rhamnosus, were fused to the downstream of the strong promoter P32 and expressed in L. brevis s3f4 as a strategy to minimize the formation of by-products. By expressing the two enzymes, a homo-fermentative pathway for lactic acid production was constructed. The lactic acid yields achieved from glucose in the transformants were 1.12 and 1.16 mol/mol, which is higher than that of the native strain (0.74 mol/mol). However, the lactic acid yield from xylose in the transformants stayed the same as that of the native strain. Enzyme assay indicated that the activity of the foreign protein FBA in the transformants was much higher than that of the native strains, but was ten times lower than that in L. rhamnosus. This result was consistent with the metabolic flux analysis, which indicated that the conversion efficiency of the expressed PFK and FBA was somewhat low. Less than 20 % of the carbons accumulated in the form of fructose-6-phosphate were converted into glyceraldehyde-3-phosphate (GAP) by the expressed PFK and FBA. Metabolic flux analysis also indicated that the enzyme phosphoketolase (XPK) played an important role in splitting the carbon flow from the pentose phosphate pathway to the phosphoketolase pathway. This study suggested that the lactic acid yield of L. brevis could be improved by constructing a homo-fermentative pathway.     

Engineering yield and rate of reductive biotransformation in <Emphasis Type="Italic">Escherichia coli</Emphasis> by partial cyclization of the pentose phosphate pathway and PTS-independent glucose transport

Optimization of yields and productivities in reductive whole-cell biotransformations is an important issue for the industrial application of such processes. In a recent study with Escherichia coli, we analyzed the reduction of the prochiral β-ketoester methyl acetoacetate by an R-specific alcohol dehydrogenase (ADH) to the chiral hydroxy ester (R)-methyl 3-hydroxybutyrate (MHB) using glucose as substrate for the generation of NADPH. Deletion of the phosphofructokinase gene pfkA almost doubled the yield to 4.8 mol MHB per mole of glucose, and it was assumed that this effect was due to a partial cyclization of the pentose phosphate pathway (PPP). Here, this partial cyclization was confirmed by ¹³C metabolic flux analysis, which revealed a negative net flux from glucose 6-phosphate to fructose 6-phosphate catalyzed by phosphoglucose isomerase. For further process optimization, the genes encoding the glucose facilitator (glf) and glucokinase (glk) of Zymomonas mobilis were overexpressed in recombinant E. coli strains carrying ADH and deletions of either pgi (phosphoglucose isomerase), or pfkA, or pfkA plus pfkB. In all cases, the glucose uptake rate was increased (30–47%), and for strains Δpgi and ΔpfkA also, the specific MHB production rate was increased by 15% and 20%, respectively. The yield of the latter two strains slightly dropped by 11% and 6%, but was still 73% and 132% higher compared to the reference strain with intact pgi and pfkA genes and expressing glf and glk. Thus, metabolic engineering strategies are presented for improving yield and rate of reductive redox biocatalysis by partial cyclization of the PPP and by increasing glucose uptake, respectively.     

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.     

Reduced Oxidative Pentose Phosphate Pathway Flux in Recombinant Xylose-Utilizing Saccharomyces cerevisiae Strains Improves the Ethanol Yield from Xylose

In recombinant, xylose-fermenting Saccharomyces cerevisiae, about 30% of the consumed xylose is converted to xylitol. Xylitol production results from a cofactor imbalance, since xylose reductase uses both NADPH and NADH, while xylitol dehydrogenase uses only NAD⁺. In this study we increased the ethanol yield and decreased the xylitol yield by lowering the flux through the NADPH-producing pentose phosphate pathway. The pentose phosphate pathway was blocked either by disruption of the GND1 gene, one of the isogenes of 6-phosphogluconate dehydrogenase, or by disruption of the ZWF1 gene, which encodes glucose 6-phosphate dehydrogenase. Decreasing the phosphoglucose isomerase activity by 90% also lowered the pentose phosphate pathway flux. These modifications all resulted in lower xylitol yield and higher ethanol yield than in the control strains. TMB3255, carrying a disruption of ZWF1, gave the highest ethanol yield (0.41 g g⁻¹) and the lowest xylitol yield (0.05 g g⁻¹) reported for a xylose-fermenting recombinant S. cerevisiae strain, but also an 84% lower xylose consumption rate. The low xylose fermentation rate is probably due to limited NADPH-mediated xylose reduction. Metabolic flux modeling of TMB3255 confirmed that the NADPH-producing pentose phosphate pathway was blocked and that xylose reduction was mediated only by NADH, leading to a lower rate of xylose consumption. These results indicate that xylitol production is strongly connected to the flux through the oxidative part of the pentose phosphate pathway.     

Engineering redox cofactor regeneration for improved pentose fermentation in Saccharomyces cerevisiae

Pentose fermentation to ethanol with recombinant Saccharomyces cerevisiae is slow and has a low yield. A likely reason for this is that the catabolism of the pentoses D-xylose and L-arabinose through the corresponding fungal pathways creates an imbalance of redox cofactors. The process, although redox neutral, requires NADPH and NAD+, which have to be regenerated in separate processes. NADPH is normally generated through the oxidative part of the pentose phosphate pathway by the action of glucose-6-phosphate dehydrogenase (ZWF1). To facilitate NADPH regeneration, we expressed the recently discovered gene GDP1, which codes for a fungal NADP+-dependent D-glyceraldehyde-3-phosphate dehydrogenase (NADP-GAPDH) (EC 1.2.1.13), in an S. cerevisiae strain with the D-xylose pathway. NADPH regeneration through an NADP-GAPDH is not linked to CO2 production. The resulting strain fermented D-xylose to ethanol with a higher rate and yield than the corresponding strain without GDP1; i.e., the levels of the unwanted side products xylitol and CO2 were lowered. The oxidative part of the pentose phosphate pathway is the main natural path for NADPH regeneration. However, use of this pathway causes wasteful CO2 production and creates a redox imbalance on the path of anaerobic pentose fermentation to ethanol because it does not regenerate NAD+. The deletion of the gene ZWF1 (which codes for glucose-6-phosphate dehydrogenase), in combination with overexpression of GDP1 further stimulated D-xylose fermentation with respect to rate and yield. Through genetic engineering of the redox reactions, the yeast strain was converted from a strain that produced mainly xylitol and CO2 from D-xylose to a strain that produced mainly ethanol under anaerobic conditions.     

Effect of phosphon-D on photosynthetic light reactions and on reactions of the oxidative and reductive pentose phosphate cycle in a reconstituted spinach (Spinacia oleracea L.) chloroplast system

Phosphon-D (tributyl-2, 4-dichlorobenzylphosphonium chloride), known as an inhibitor of gibberellin biosynthesis, enhances photosynthetic electron transport by up to 200%, with Fe(CN) ₆ ^3- and NADP⁺ being the electron acceptors. Maximum stimulation is reached at phosphon-D concentrations around 2–5 M. At the same time photosynthetic ATP formation is gradually inhibited. Phosphon-D concentrations over 0.1 mM inhibit electron transport. The uncoupling activity of phosphon-D is manifested by inhibition of noncyclic ATP synthesis and by stimulation of light-induced electron flow. The inhibition of ATP synthesis drastically decreases photosynthetic carbon assimilation in a reconstituted spinach chloroplast system. The two ATP-dependent kinase reactions of the reductive pentose phosphate cycle become the rate-limiting steps. On the other hand a stimulated photoelectron transport increases the NADPH/NADP⁺ ratio, resulting in a drastic inhibition of chloroplast glucose-6-phosphate dehydrogenase (EC 1.1.1.49), the key enzyme of the oxidative pentose phosphate cycle. When light-induced electron flow is inhibited by high phosphon-D concentrations and the NADPH/NADP⁺ ratio is low, the light-dependent inhibition of glucose-6-phosphate dehydrogenase is gradually abolished.Abbreviations AMO-1618 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidinecarboxylate methyl chloride - B-Nine N-dimethylaminosuccinamic acid - CCC (2-chloroethyl)-trimethylammonium chloride - DCMU 3-(3,4-dichlorophenyl)-1, 1-dimethyl urea - DCPIP dichlorophenolindophenol - G-6-PDH glucose-6-phosphate dehydrogenase - FBP fructose bisphosphate - F-6-P fructose-6-phosphate - 3-PGA 3-phosphoglyceric acid - Posphon-D tributyl-2,4-dichlorobenzylphosphonium chloride - PMP pentose monophosphates - PPC pentose phosphate cycle - RuBP ribulose bisphosphate - Ru-5-P ribulose-5-phosphate Dedicated to Prof. Dr. Drs.h.c. Adolf Butenandt on the occasion of his 75. birthday     

Metabolic Fluxes in Corynebacterium glutamicum during Lysine Production with Sucrose as Carbon Source

Metabolic fluxes in the central metabolism were determined for lysine-producing Corynebacterium glutamicum ATCC 21526 with sucrose as a carbon source, providing an insight into molasses-based industrial production processes with this organism. For this purpose, ¹³C metabolic flux analysis with parallel studies on [1-¹³C^Fru]sucrose, [1-¹³C^Glc]sucrose, and [¹³C₆^Fru]sucrose was carried out. C. glutamicum directed 27.4% of sucrose toward extracellular lysine. The strain exhibited a relatively high flux of 55.7% (normalized to an uptake flux of hexose units of 100%) through the pentose phosphate pathway (PPP). The glucose monomer of sucrose was completely channeled into the PPP. After transient efflux, the fructose residue was mainly taken up by the fructose-specific phosphotransferase system (PTS) and entered glycolysis at the level of fructose-1,6-bisphosphate. Glucose-6-phosphate isomerase operated in the gluconeogenetic direction from fructose-6-phosphate to glucose-6-phosphate and supplied additional carbon (7.2%) from the fructose part of the substrate toward the PPP. This involved supply of fructose-6-phosphate from the fructose part of sucrose either by PTS^Man or by fructose-1,6-bisphosphatase. C. glutamicum further exhibited a high tricarboxylic acid (TCA) cycle flux of 78.2%. Isocitrate dehydrogenase therefore significantly contributed to the total NADPH supply of 190%. The demands for lysine (110%) and anabolism (32%) were lower than the supply, resulting in an apparent NADPH excess. The high TCA cycle flux and the significant secretion of dihydroxyacetone and glycerol display interesting targets to be approached by genetic engineers for optimization of the strain investigated.     

Modification of glycolysis and its effect on the production of l-threonine in Escherichia coli

High concentrations of acetate, the main by-product of Escherichia coli (E. coli) high cell density culture, inhibit bacterial growth and l-threonine production. Since metabolic overflux causes acetate accumulation, we attempted to reduce acetate production by redirecting glycolysis flux to the pentose phosphate pathway by deleting the genes encoding phosphofructokinase (pfk) and/or pyruvate kinase (pyk) in an l-threonine-producing strain of E. coli, THRD. pykF, pykA, pfkA, and pfkB deletion mutants produced less acetate (9.44 ± 0.83, 3.86 ± 0.88, 0.30 ± 0.25, and 6.99 ± 0.85 g/l, respectively) than wild-type THRD cultures (19.75 ± 0.93 g/l). THRDΔpykF and THRDΔpykA produced 11.05 and 5.35 % more l-threonine, and achieved a 10.91 and 5.60 % higher yield on glucose, respectively. While THRDΔpfkA grew more slowly and produced less l-threonine than THRD, THRDΔpfkB produced levels of l-threonine (102.28 ± 2.80 g/l) and a yield on glucose (0.34 g/g) similar to that of THRD. The dual deletion mutant THRDΔpfkBΔpykF also achieved low acetate (7.42 ± 0.81 g/l) and high l-threonine yields (111.37 ± 2.71 g/l). The level of NADPH in THRDΔpfkA cultures was depressed, whereas all other mutants produced more NADPH than THRD did. These results demonstrated that modification of glycolysis in E. coli THRD reduced acetate production and increased accumulation of l-threonine.     

Mutational Analyses of Glucose Dehydrogenase and Glucose-6-Phosphate Dehydrogenase Genes in Pseudomonas fluorescens Reveal Their Effects on Growth and Alginate Production

The biosynthesis of alginate has been studied extensively due to the importance of this polymer in medicine and industry. Alginate is synthesized from fructose-6-phosphate and thus competes with the central carbon metabolism for this metabolite. The alginate-producing bacterium Pseudomonas fluorescens relies on the Entner-Doudoroff and pentose phosphate pathways for glucose metabolism, and these pathways are also important for the metabolism of fructose and glycerol. In the present study, the impact of key carbohydrate metabolism enzymes on growth and alginate synthesis was investigated in P. fluorescens. Mutants defective in glucose-6-phosphate dehydrogenase isoenzymes (Zwf-1 and Zwf-2) or glucose dehydrogenase (Gcd) were evaluated using media containing glucose, fructose, or glycerol. Zwf-1 was shown to be the most important glucose-6-phosphate dehydrogenase for catabolism. Both Zwf enzymes preferred NADP as a coenzyme, although NAD was also accepted. Only Zwf-2 was active in the presence of 3 mM ATP, and then only with NADP as a coenzyme, indicating an anabolic role for this isoenzyme. Disruption of zwf-1 resulted in increased alginate production when glycerol was used as the carbon source, possibly due to decreased flux through the Entner-Doudoroff pathway rendering more fructose-6-phosphate available for alginate biosynthesis. In alginate-producing cells grown on glucose, disruption of gcd increased both cell numbers and alginate production levels, while this mutation had no positive effect on growth in a non-alginate-producing strain. A possible explanation is that alginate synthesis might function as a sink for surplus hexose phosphates that could otherwise be detrimental to the cell.     

Evidence for Activation of the Oxidative Pentose Phosphate Pathway during Photosynthetic Assimilation of NO(3) but Not NH(4) by a Green Alga

Addition of NO₃⁻ to N-limited Selenastrum minutum during photosynthesis resulted in an immediate drop in the NADPH/NADP ratio and a slower increase of the NADH/NAD ratio. These changes were accompanied by a rapid decrease in glucose-6-phosphate and increase in 6-phosphogluconate, indicating activation of glucose-6-phosphate dehydrogenase and a role for the oxidation pentose phosphate pathway during photosynthetic NO₃⁻ assimilation. In contrast, the short-term changes in pyridine nucleotides and metabolites during photosynthetic assimilation of NH₄⁺ were not consistent with a stimulation of the oxidative pentose phosphate pathway.     

Evidence for a pentose phosphate pathway in Helicobacter pylori

Abstract Evidence for the presence of enzymes of the pentose phosphate pathway in Helicobacter pylori was obtained using ³¹P nuclear magnetic resonance spectroscopy. Activities of enzymes which are part of the oxidative and non-oxidative phases of the pathway were observed directly in incubations of bacterial lysates with pathway intermediates. Generation of NADPH and 6-phosphogluconate from NADP⁺ and glucose 6-phosphate indicated the presence of glucose 6-phosphate dehydrogenase and 6-phosphogluconolactonase. Reduction of NADP⁺ with production of ribulose 5-phosphate from 6-phosphogluconate revealed 6-phosphogluconate dehydrogenase activity. Phosphopentose isomerase and transketolase activities were observed in incubations containing ribulose 5-phosphate and xylulose 5-phosphate, respectively. The formation of erythrose 4-phosphate from xylulose 5-phosphate and ribose 5-phosphate suggested the presence of transaldolase. The activities of this enzyme and triosephosphate isomerase were observed directly in incubations of bacterial lysates with dihydroxyacetone phosphate and sedoheptulose 7-phosphate. Glucose-6-phosphate isomerase activity was measured in incubations with fructos 6-phosphate. The presence of these enzymes in H. pylori suggested the existence of a pentose phosphate pathway in the bacterium, possibly as a mechanism to provide NADPH for reductive biosynthesis and ribose 5-phosphate for synthesis of nucleic acids.     

Adjustment of Trehalose Metabolism in Wine Saccharomyces cerevisiae Strains To Modify Ethanol Yields

The ability of Saccharomyces cerevisiae to efficiently produce high levels of ethanol through glycolysis has been the focus of much scientific and industrial activity. Despite the accumulated knowledge regarding glycolysis, the modification of flux through this pathway to modify ethanol yields has proved difficult. Here, we report on the systematic screening of 66 strains with deletion mutations of genes encoding enzymes involved in central carbohydrate metabolism for altered ethanol yields. Five of these strains showing the most prominent changes in carbon flux were selected for further investigation. The genes were representative of trehalose biosynthesis (TPS1, encoding trehalose-6-phosphate synthase), central glycolysis (TDH3, encoding glyceraldehyde-3-phosphate dehydrogenase), the oxidative pentose phosphate pathway (ZWF1, encoding glucose-6-phosphate dehydrogenase), and the tricarboxylic acid (TCA) cycle (ACO1 and ACO2, encoding aconitase isoforms 1 and 2). Two strains exhibited lower ethanol yields than the wild type (tps1Δ and tdh3Δ), while the remaining three showed higher ethanol yields. To validate these findings in an industrial yeast strain, the TPS1 gene was selected as a good candidate for genetic modification to alter flux to ethanol during alcoholic fermentation in wine. Using low-strength promoters active at different stages of fermentation, the expression of the TPS1 gene was slightly upregulated, resulting in a decrease in ethanol production and an increase in trehalose biosynthesis during fermentation. Thus, the mutant screening approach was successful in terms of identifying target genes for genetic modification in commercial yeast strains with the aim of producing lower-ethanol wines.     

Redirection of the Glycolytic Flux Enhances Isoprenoid Production in Saccharomyces cerevisiae

Sufficient supply of reduced nicotinamide adenine dinucleotide phosphate (NADPH) is a prerequisite of the overproduction of isoprenoids and related bioproducts in Saccharomyces cerevisiae. Although S. cerevisiae highly depends on the oxidative pentose phosphate (PP) pathway to produce NADPH, its metabolic flux toward the oxidative PP pathway is limited due to the rigid glycolysis flux. To maximize NADPH supply for the isoprenoid production in yeast, upper glycolytic metabolic fluxes are reduced by introducing mutations into phosphofructokinase (PFK) along with overexpression of ZWF1 encoding glucose‐6‐phosphate (G6P) dehydrogenase. The PFK mutations (Pfk1 S724D and Pfk2 S718D) result in less glycerol production and more accumulation of G6P, which is a gateway metabolite toward the oxidative PP pathway. When combined with the PFK mutations, overexpression of ZWF1 caused substantial increases of [NADPH]/[NADP⁺] ratios whereas the effect of ZWF1 overexpression alone in the wild‐type strain is not noticeable. Also, the introduction of ZWF1 overexpression and the PFK mutations into engineered yeast overexpressing acetyl‐CoA C‐acetyltransferase (ERG10), truncated HMG‐CoA reductase isozyme 1 (tHMG1), and amorphadiene synthase (ADS) leads to a titer of 497 mg L^–1 of amorphadiene (3.7‐fold over the parental strain). These results suggest that perturbation of upper glycolytic fluxes, in addition to ZWF1 overexpression, is necessary for efficient NADPH supply through the oxidative PP pathway and enhanced production of isoprenoids by engineered S. cerevisiae.     

Replacing Escherichia coli NAD-dependent glyceraldehyde 3-phosphate dehydrogenase (GAPDH) with a NADP-dependent enzyme from Clostridium acetobutylicum facilitates NADPH dependent pathways

Reactions requiring reducing equivalents, NAD(P)H, are of enormous importance for the synthesis of industrially valuable compounds such as carotenoids, polymers, antibiotics and chiral alcohols among others. The use of whole-cell biocatalysis can reduce process cost by acting as catalyst and cofactor regenerator at the same time; however, product yields might be limited by cofactor availability within the cell. Thus, our study focussed on the genetic manipulation of a whole-cell system by modifying metabolic pathways and enzymes to improve the overall production process. In the present work, we genetically engineered an Escherichia coli strain to increase NADPH availability to improve the productivity of products that require NADPH in its biosynthesis. The approach involved an alteration of the glycolysis step where glyceraldehyde-3-phosphate (GAP) is oxidized to 1,3 bisphophoglycerate (1,3-BPG). This reaction is catalyzed by NAD-dependent endogenous glyceraldehyde-3-phosphate dehydrogenase (GAPDH) encoded by the gapA gene. We constructed a recombinant E. coli strain by replacing the native NAD-dependent gapA gene with a NADP-dependent GAPDH from Clostridium acetobutylicum, encoded by the gene gapC. The beauty of this approach is that the recombinant E. coli strain produces 2 mol of NADPH, instead of NADH, per mole of glucose consumed. Metabolic flux analysis showed that the flux through the pentose phosphate (PP) pathway, one of the main pathways that produce NADPH, was reduced significantly in the recombinant strain when compared to that of the parent strain. The effectiveness of the NADPH enhancing system was tested using the production of lycopene and epsilon-caprolactone as model systems using two different background strains. The recombinant strains, with increased NADPH availability, consistently showed significant higher productivity than the parent strains.     

Metabolic engineering of Corynebacterium glutamicum for production of sunscreen shinorine

Ultraviolet-absorbing chemicals are useful in cosmetics and skin care to prevent UV-induced skin damage. We demonstrate here that heterologous production of shinorine, which shows broad absorption maxima in the UV-A and UV-B region. A shinorine producing Corynebacterium glutamicum strain was constructed by expressing four genes from Actinosynnema mirum DSM 43827, which are responsible for the biosynthesis of shinorine from sedoheptulose-7-phosphate in the pentose phosphate pathway. Deletion of transaldolase encoding gene improved shinorine production by 5.2-fold. Among the other genes in pentose phosphate pathway, overexpression of 6-phosphogluconate dehydrogenase encoding gene further increased shinorine production by 60% (19.1 mg/L). The genetic engineering of the pentose phosphate pathway in C. glutamicum improved shinorine production by 8.3-fold in total, and could be applied to produce the other chemicals derived from sedoheptulose-7-phosphate.     

植物戊糖磷酸途径及其两个关键酶的研究进展

戊糖磷酸途径是植物体中糖代谢的重要途径,主要生理功能是产生供还原性生物合成需要的NADPH,可供核酸代谢的磷酸戊糖以及一些中间产物可参与氨基酸合成和脂肪酸合成等.葡萄糖-6-磷酸脱氢酶和6-磷酸葡萄糖酸脱氢酶是戊糖磷酸途径的两个关键酶,广泛的分布于高等植物的胞质和质体中.本文综述了植物戊糖磷酸途径及其两个关键酶的分子生物学的研究进展,讨论了该途径在植物生长发育和环境胁迫应答中的作用.