Changes in enzymic activities of nucleoside diphosphate sugar interconversions during differentiation of cambium to xylem in sycamore and poplar.

During the transition from primary wall formation to secondary thickening there is a marked shift in the synthesis of pectin, hemicellulose and cellulose. The activities of the enzymes [UDP-D-galactose 4-epimerase (EC 5.1.3.2)8 UDP-l-arabinose 4-epimerase (EC 5.1.3.5), UDP-D-glucose dehydrogenase (EC 1.1.1.22) and UDP-D--glucuronate decarboxylase (EC 4.1.1.35)] were measured in cambial cells, differentiating xylem cells and differentiated xylem cells isolated from sycamore and poplar trees, and phloem cells from poplar. At the final stage of the differentiation of cambium to xylem there was a decrease in activity of the enzymes directly involved in producing the soluble precursors of pectin (DUP-D-galactose 4-epimerase and UDP-L-arabinose 4-epimerase and an increase in those producing the precursors of hemicellulose (UDP-D-glucose dehydrogenase and UDP-D-glucuronate decarboxylase). These results strongly suggest ahat the changes were correlated with the differences observed in the chemical composition of the wall during development. The changes found in the catalytic activity of the enzymes of nucleoside diphosphate sugar interconversion exert a coarse control over the synthesis of pectin and hemicelluloses. The tissues at all stages of development contained the necessary enzyme activities to produce all the precursors of pectin and hemicellulose, even at the final stage of differentiation when no pectin was formed.     

Changes in enzymic activities of UDP-D-glucuronate decarboxylase and UDP-D-xylose 4-epimerase during cell division and xylem differentiation in

The time course of the specific activities of UDP-D-glucuronate decarboxylase (E.C. 4.1.1.35) and UDP-D-xylose 4-epimerase (E.C. 5.1.3.5) have     

Changes in enzymic activities of nucleoside diphosphate sugar interconversions during differentiation of cambium to xylem in pine and fir.

A protein fraction [precipitate obtained between 40 and 65% (NH4)2SO4 satn.] prepared from cambial cells, differentiating xylem cells and differentiated xylem cells of pine and fir trees contained all the enzymes required for the nucleoside diphosphate sugar interconversions. By using UDP-D-[U-14C]glucose or UDP-D-[U-14C]galactose, UDP-D-[U-14C-]glucuronic acid and UDP-D-[U-14C]xylose as substrates, the activities of UDP-D-galactose 4-epimerase (DC 5.1.3.2), UDP-D-xylose 4-epimerase(EC 5.1.3.5), UDP-D-glucose dehydrogenase (EC 1.1.1.22) and UDP-D-glucuronate 4-epimerase (EC5.1.3.6), UDP-d-glucuronate decarboxylase (EC 4.1.1.35) were measured at different stages of cell-wall development. The specific activities and the activities per cell of these enzymes varied during differentiation of cambium to xylem according to the type polysaccharide synthesized. Variations were also found between the two species investigated. These data, compared with those obtained in out previous work on angiosperms [see the preceding paper, Dalessandro & Northcote (1977) Biochem. J. 162, 267-279], suggest that some control of polysaccharide synthesis operates at the level of the formation of the precursors of pectin and hemicellulose syntheses.     

Functional analysis of Arabidopsis thaliana RHM2/MUM4, a multidomain protein involved in UDP-D-glucose to UDP-L-rhamnose conversion

UDP-L-rhamnose is required for the biosynthesis of cell wall rhamnogalacturonan-I, rhamnogalacturonan-II, and natural compounds in plants. It has been suggested that the RHM2/MUM4 gene is involved in conversion of UDP-D-glucose to UDP-L-rhamnose on the basis of its effect on rhamnogalacturonan-I-directed development in Arabidopsis thaliana. RHM2/MUM4-related genes, RHM1 and RHM3, can be found in the A. thaliana genome. Here we present direct evidence that all three RHM proteins have UDP-D-glucose 4,6-dehydratase, UDP-4-keto-6-deoxy-D-glucose 3,5-epimerase, and UDP-4-keto-L-rhamnose 4-keto-reductase activities in the cytoplasm when expressed in the yeast Saccharomyces cerevisiae. Functional domain analysis revealed that the N-terminal region of RHM2 (RHM2-N; amino acids 1-370) has the first activity and the C-terminal region of RHM2 (RHM2-C; amino acids 371-667) has the two following activities. This suggests that RHM2 converts UDP-d-glucose to UDP-L-rhamnose via an UDP-4-keto-6-deoxy-D-glucose intermediate. Site-directed mutagenesis of RHM2 revealed that mucilage defects in MUM4-1 and MUM4-2 mutant seeds of A. thaliana are caused by abolishment of RHM2 enzymatic activity in the mutant strains and furthermore, that the GXXGXX(G/A) and YXXXK motifs are important for enzymatic activity. Moreover, a kinetic analysis of purified His(6)-tagged RHM2-N protein revealed 5.9-fold higher affinity of RHM2 for UDP-D-glucose than for dTDP-D-glucose, the preferred substrate for dTDP-D-glucose 4,6-dehydratase from bacteria. RHM2-N activity is strongly inhibited by UDP-L-rhamnose, UDP-D-xylose, and UDP but not by other sugar nucleotides, suggesting that RHM2 maintains cytoplasmic levels of UDP-D-glucose and UDP-L-rhamnose via feedback inhibition by UDP-L-rhamnose and UDP-D-xylose.     

Reconstruction of de novo pathway for synthesis of UDP-glucuronic acid and UDP-xylose from intrinsic UDP-glucose in Saccharomyces cerevisiae

UDP-D-glucuronic acid and UDP-D-xylose are required for the biosynthesis of glycosaminoglycan in mammals and of cell wall polysaccharides in plants. Given the importance of these glycans to some organisms, the development of a system for production of UDP-D-glucuronic acid and UDP-D-xylose from a common precursor could prove useful for a number of applications. The budding yeast Saccharomyces cerevisiae lacks an endogenous ability to synthesize or consume UDP-D-glucuronic acid and UDP-D-xylose. However, yeast have a large cytoplasmic pool of UDP-D-glucose that could be used to synthesize cell wall beta-glucan, as a precursor of UDP-D-glucuronic acid and UDP-D-xylose. Thus, if a mechanism for converting the precursors into the end-products can be identified, yeast may be harnessed as a system for production of glycans. Here we report a novel S. cerevisiae strain that coexpresses the Arabidopsis thaliana genes UGD1 and UXS3, which encode a UDP-glucose dehydrogenase (AtUGD1) and a UDP-glucuronic acid decarboxylase (AtUXS3), respectively, which are required for the conversion of UDP-D-glucose to UDP-D-xylose in plants. The recombinant yeast strain was capable of converting UDP-D-glucose to UDP-D-glucuronic acid, and UDP-D-glucuronic acid to UDP-D-xylose, in the cytoplasm, demonstrating the usefulness of this yeast system for the synthesis of glycans. Furthermore, we observed that overexpression of AtUGD1 caused a reduction in the UDP-D-glucose pool, whereas coexpression of AtUXS3 and AtUGD1 did not result in reduction of the UDP-D-glucose pool. Enzymatic analysis of the purified hexamer His-AtUGD1 revealed that AtUGD1 activity is strongly inhibited by UDP-D-xylose, suggesting that AtUGD1 maintains intracellular levels of UDP-D-glucose in cooperation with AtUXS3 via the inhibition of AtUGD1 by UDP-D-xylose.     

Role of Gne and GalE in the virulence of Aeromonas hydrophila serotype O34

The mesophilic Aeromonas hydrophila AH-3 (serotype O34) strain shows two different UDP-hexose epimerases in its genome: GalE (EC 3.1.5.2) and Gne (EC 3.1.5.7). Similar homologues were detected in the different mesophilic Aeromonas strains tested. GalE shows only UDP-galactose 4-epimerase activity, while Gne is able to perform a dual activity (mainly UDP-N-acetyl galactosamine 4-epimerase and also UDP-galactose 4-epimerase). We studied the activities in vitro of both epimerases and also in vivo through the lipopolysaccharide (LPS) structure of A. hydrophila gne mutants, A. hydrophila galE mutants, A. hydrophila galE-gne double mutants, and independently complemented mutants with both genes. Furthermore, the enzymatic activity in vivo, which renders different LPS structures on the mentioned A. hydrophila mutant strains or the complemented mutants, allowed us to confirm a clear relationship between the virulence of these strains and the presence/absence of the O34 antigen LPS.     

Changes in enzyme activities involved in formation and interconversion of UDP-sugars during the cell cycle in a synchronous culture of Catharanthus roseus

Changes in the activities of enzymes involved in UDP-sugar formation [UDP-glucose pyrophosphorylase (EC 2.7.7.9), sucrose synthase (EC 2.4.1.13) and UDP-glucuronic acid pyrophosphorylase (EC 2.7.7.44)], and interconversion [UDP-glucuse 4-epimerase (EC 5.1.3.2), UDP-glucose dehydrogenase (EC 1.1.1.22), UDP-glucuronic acid decarboxylase (EC 4.1.1.35) and UDP-xylose 4-epimerase (EC 5.1.3.5)] were investigated during the cell cycle in a synchronous culture of Catharanthus roseus (L.) G. Don. The specific activities of UDP-glucose pyrophosphorylase and UDP-glucose 4-epimerase increased in the G2 phase before the first cell division, and those of sucrose synthase, UDP-glucose dehydrogenase and UDP-glucuronic acid pyrophosphorylase increased in the G1 phase after the first cell division. However, during the cell cycle, UDP-glucuronic acid decarboxylase and UDP-xylose 4-epimerase did not change significantly in their specific activities. Changes in enzyme activities are discussed in relation to those reported previously for cell wall composition (S. Amino et al. 1984. Physiologia Plantarum 60: 326–332).     

A quantitative cytochemical study of UDP-D-glucose: NAD-oxidoreductase (E.C. 1.1.1.22) activity during stelar differentiation in Pisum sativum L. cv Meteor

A quantitative cytochemical assay for UDP-D-glucose dehydrogenase (UDPGD) activity employing scanning and integrating microdensitometry has been revised and applied to a study of this enzyme during the initiation of secondary cell wall biosynthesis during the formation of primary vascular tissues in roots of Pisum sativum L. cv Meteor. The reaction involves the use of NBT as final electron acceptor and is inhibited 10-fold by either 10 mM UDP-D-xylose or 25 mM UDP-D-glucuronic acid, two molecules involved in feed-back inhibition of UDPGD activity in vivo. UDPGD is a far-from equilibrium enzyme representing a flux-generating step in the biosynthesis of precursors for hemicelluloses involved in secondary cell wall construction, and can be demonstrated to increase sharply in activity in cells of the developing primary vascular elements. This changed activity occurs 18-20 cells back from the root cap junction and coincides with the first cells containing the activated programme for secondary cell wall synthesis.     

Enzymic activities of carbohydrate,purine, and pyrimidine metabolism in the Anaeroplasmataceae (class Mollicutes)

Cell-free extracts of two strictly anaerobic mollicutes, Anaeroplasma intermedium 5LA and Asteroleplasma anaerobium 161^T, were tested for enzymic activities of intracellular carbohydrate metabolism. Asteroleplasma anaerobium was also tested for enzymes of purine and pyrimidine metabolism. Both organisms had enzymic activities associated with the nonoxidative portion of the pentose phosphate pathway, and with the Embden-Meyerhoff-Parnas pathway. The 6-phosphofructokinase (PFK) of Asteroleplasma anaerobium was ATP-dependent, whereas the PFK of Anaeroplasma intermedium was PP_i-dependent. The two anaerobic mollicutes also differed with respect to the enzymes that converted phosphoenolpyruvate (PEP) to pyruvate; Anaeroplasma intermedium had pyruvate kinase activity, but Asteroleplasma anaerobium had pyruvate, orthophosphate dikinase activity (PP_i-dependent). Both organisms had lactate dehydrogenase activity which was activated by fructose 1,6-bisphosphate (Fru-1,6-P ₂). Anaeroplasma intermedium had activity for PEP carboxykinase (activated by Fru-1,6-P ₂), but Asteroleplasma anaerobium did not. PEP carboxytransphosphorylase activity was not detected in either organism. Anaeroplasma intermedium had malate dehydrogenase and isocitrate dehydrogenase activities, but it had no activities for the three other tricarboxylic acid cycle enzymes examined; Asteroleplasma anaerobium had malate dehydrogenase activity only. Asteroleplasma anaerobium had enzymic activities for the interconversion of purine nucleobases, (deoxy)ribonucleosides, and (deoxy)ribomononucleotides, including PP_i-dependent nucleoside kinase, reported heretofore only in some other mollicutes. Asteroleplasma anaerobium could synthesize dTDP by the thymine salvage pathway if deoxyribose 1-phosphate was provided, and it had dUTPase, ATPase, and dCMP kinase activities. It lacked (deoxy)cytidine deaminase, dCMP deaminase, and deoxycytidine kinase activities.Abbreviations EMP Embden-Meyerhof-Parnas - ICDH isocitrate dehydrogenase - LDH lactate dehydrogenase - PEP phosphoenolpyruvate - PFK phosphofructokinase - PPDK pyruvate, orthophosphate dikinase - TCA cycle tricarboxylic acid cycle Note: Other abbreviations used are as per the instruction to authors, or the reference cited therein (Eur J Biochem 1:259), or Biochem J 120:449 (which supercedes a portion of the first reference)     

Depletion of UDP-D-apiose/UDP-D-xylose synthases results in rhamnogalacturonan-II deficiency, cell wall thickening, and cell death in higher plants

D-apiose serves as the binding site for borate cross-linking of rhamnogalacturonan II (RG-II) in the plant cell wall, and biosynthesis of D-apiose involves UDP-D-apiose/UDP-D-xylose synthase catalyzing the conversion of UDP-D-glucuronate to a mixture of UDP-D-apiose and UDP-D-xylose. In this study we have analyzed the cellular effects of depletion of UDP-D-apiose/UDP-D-xylose synthases in plants by using virus-induced gene silencing (VIGS) of NbAXS1 in Nicotiana benthamiana. The recombinant NbAXS1 protein exhibited UDP-D-apiose/UDP-D-xylose synthase activity in vitro. The NbAXS1 gene was expressed in all major plant organs, and an NbAXS1-green fluorescent protein fusion protein was mostly localized in the cytosol. VIGS of NbAXS1 resulted in growth arrest and leaf yellowing. Microscopic studies of the leaf cells of the NbAXS1 VIGS lines revealed cell death symptoms including cell lysis and disintegration of cellular organelles and compartments. The cell death was accompanied by excessive formation of reactive oxygen species and by induction of various protease genes. Furthermore, abnormal wall structure of the affected cells was evident including excessive cell wall thickening and wall gaps. The mutant cell walls contained significantly reduced levels of D-apiose as well as 2-O-methyl-L-fucose and 2-O-methyl-D-xylose, which serve as markers for the RG-II side chains B and A, respectively. These results suggest that VIGS of NbAXS1 caused a severe deficiency in the major side chains of RG-II and that the growth defect and cell death was likely caused by structural alterations in RG-II due to a D-apiose deficiency.     

The effect of submergence,ethylene and gibberellin on polyamines and their biosynthetic enzymes in deepwater-rice internodes

Submergence and treatment with ethylene or gibberellic acid (GA₃) stimulates rapid growth in internodes of deepwater rice (Oryza sativa L. cv. Habiganj Aman II). This growth is based on greatly enhanced rate of cell-division activity in the intercalary meristem (IM) and on increased cell elongation. We chose polyamine biosynthesis as a biochemical marker for cell-division activity in the IM of rice stems. Upon submergence of the plant, the activity of S-adenosylmethionine decarboxylase (SAMDC; EC 4.1.1.50) in the IM increased six- to tenfold within 8 h; thereafter, SAMDC activity declined. Arginine decarboxylase (ADC; EC 4.1.1.19) showed a similar but less pronounced increase in activity. The activity of ornithine decarboxylase (ODC; EC 4.1.1.17) in the IM was not affected by submergence. The levels of putrescine and spermidine also rose in the IM of submerged, whole plants while the concentration of spermine remained low. The increase in SAMDC activity was localized in the IM while the activity of ADC rose both in the node and the IM above it. The node also contained low levels of ODC activity which increased slightly following submergence. Increased activities of polyamine-synthesizing enzymes in the nodal region of submerged plants probably resulted from the promotion of adventitious root formation in the node. Treatment of excised rice-stem sections with ethylene or GA₃ enhanced the activities of SAMDC and ADC in the IM and inhibited the decline in the levels of putrescine and spermidine. We conclude that SAMDC and perhaps also ADC may serve as biochemical markers for the enhancement of cell-division activity in the IM of deepwater rice.Abbreviations ADC arginine decarboxylase - GA gibberellin - IM intercalary meristem - ODC ornithine decarboxylase - SAM S-adenosylmethionine - SAMDC SAM decarboxylase     

Pyrimidine ribonucleoside catabolic enzyme activities ofPseudomonas pickettii

Pyrimidine ribonucleoside catabolic enzyme activities of the opportunistic pathogenPseudomonas pickettii were examined. Of the pyrimidine and related compounds tested, only dihydrouracil (nitrogen source) and ribose (carbon source) supported growth. Thin-layer chromatographic separation of the uridine and cytidine catabolities produced byP. pickettii extracts indicated that this pseudomonad contained nucleoside hydrolase activity. Its presence was confirmed by enzyme assay. Hydrolase activity was elevated in both glucose- and ribose-grown cells relative to succinate-grown cells. Nucleoside hydrolase activity was depressed when dihydrouracil served as a nitrogen source. Cytosine deaminase activity was present in extracts prepared from succinate-, glucose- or ribose-grown cells when (NH₄)₂SO₄ served as the nitrogen source although cells grown on glucose or ribose exhibited a higher enzyme activity. Cytosine deaminase activity was not detected in extracts prepared from cells grown on dihydrouracil as a nitrogen source. Both dihydropyrimidine dehydrogenase and dihydropyrimidinase activities were measurable inP. pickettii. The dehydrogenase activity was higher with NADH than with NADPH as its nicotinamide cofactor when uracil served as its substrate. Carbon source did not affect dehydrogenase or dihydropyrimidinase activity greatly but both activities were diminished in cells grown on the nitrogen source dihydrouracil.     

Metabolic regulation of carbon and electron flow as a function of pH during growth of Sarcina ventriculi

The physiology and biochemistry of Sarcina ventriculi was studied in order to determine adaptations made by the organism to changes in environmental pH. The organism altered carbon and electron flow from acetate, formate and ethanol production at neutral pH, to predominantly ethanol production at pH 3.0. Increased levels of pyruvate dehydrogenase (relative to pyruvate decarboxylase) and acetaldehyde dehydrogenase occurred when the organism was grown at neutral pH, indicating the predominance of carbon flux through the oxidative branch of the pathway for pyruvate metabolism. When the organism was grown at acid pH, there was a significant increase in pyruvate decarboxylase levels and a decrease in acetaldehyde dehydrogenase, causing flux through the non-oxidative branch of the pathway. CO₂ reductase and formate dehydrogenase were not regulated as a function of growth pH. Pyruvate dehydrogenase possessed Michaelis-Menten kinetics for pyruvate with an apparent K _m of 2.5 mM, whereas pyruvate decarboxylase exhibited sigmoidal kinetics, with a S_0.5 of 12.0 mM. Differences in total protein banding patterns from cells grown at pH extremes suggested that synthesis of pyruvate decarboxylase and other enzymes was in part responsible for metabolic regulation of the fermentation products formed.     

Xylan synthetase activity in differentiated xylem cells of sycamore trees (Acer pseudoplatanus)

Particulate enzymic preparations obtained from homogenates of differentiated xylem cells isolated from sycamore trees, catalyzed the formation of a radioactive xylan in the presence of UDP-D-[U-¹⁴C]xylose as substrate. The synthesized xylan was not dialyzable through Visking cellophane tubing. Successive extraction with cold water, hot water and 5% NaOH dissolved respectively 15, 5 and 80% of the radioactive polymer. Complete acid hydrolysis of the water-insoluble polysaccharide synthesized from UDP-D-[U-¹⁴C]xylose released all the radioactivity as xylose. -1,4-Xylodextrins, degree of polymerization 2, 3, 4, 5 and 6, were obtained by partial acid hydrolysis (fuming HCl or 0.1 M HCl) of radioactive xylan. The polymer was hydrolysed to xylose, xylobiose and xylotriose by Driselase which contains 1,4- xylanase activities. Methylation and then hydrolysis of the xylan released two methylated sugars which were identified as di-O-methyl[¹⁴C]xylose and tri-O-methyl-[¹⁴C]xylose, suggesting a 14-linked polymer. The linkage was confirmed by periodate oxidation studies. The apparent K_m value of the synthetase for UDP-D-xylose was 0.4 mM. Xylan synthetase activity was not potentiated in the presence of a detergent. The enzymic activity was stimulated by Mg²⁺ and Mn²⁺ ions, although EDTA in the range of concentrations between 0.01 and 1 mM did not affect the reaction rate. It appears that the xylan synthetase system associated with membranes obtained from differentiated xylem cells of sycamore trees may serve for catalyzing the in vivo synthesis of the xylan main chain during the biogenesis of the plant cell wall.     

Effect of N deficiency on leaf growth and cell wall peroxidase activity in contrasting maize genotypes

Two maize genotypes differing in leaf elongation rate (high-LER and low-LER) were used for the investigation of the effects of nitrogen deficiency on leaf growth and development and activity of enzyme cell wall peroxidase in the leaf growth zone. Plants were grown in a growth cabinet in perlite as a substrate and watered with complete N-NO₃ solution (+N) and N-NO₃ deficient solution (–N). Comparison between the investigated genotypes showed that final leaf length in both N treatments was related with LER, but not with the duration of leaf elongation. Faster leaf elongation rate in high-LER compared with low-LER genotype, was associated with longer growth zone, a bigger number of cells in it, and higher cell flux rate, although cell elongation rate was similar in both genotypes. These lines of evidence indirectly indicated that leaves of the faster growing genotype were characterized by higher meristematic activity. Nitrogen deficiency reduced the flux of cells and cell elongation rate, length of cell division zone and the number of cells in whole zone, significantly for both genotypes, although duration of cell elongation was increased and final epidermal cell length was unchanged. These results showed that N deficiency reduced both cell division and cell elongation, which in turn resulted in decreased leaf length and prolonged time for leaf development. Nitrogen deficiency significantly increased both bulk and segmental cell wall peroxidase activity in the growth zone of both investigated genotypes, thus showing an interaction between leaf growth cessation and enzyme activity.     

The biosynthesis of D-Galacturonate in plants. functional cloning and characterization of a membrane-anchored UDP-D-Glucuronate 4-epimerase from Arabidopsis

Pectic cell wall polysaccharides owe their high negative charge to the presence of D-galacturonate, a monosaccharide that appears to be present only in plants and some prokaryotes. UDP-D-galacturonate, the activated form of this sugar, is known to be formed by the 4-epimerization of UDP-D-glucuronate; however, no coding regions for the epimerase catalyzing this reaction have previously been described in plants. To better understand the mechanisms by which precursors for pectin synthesis are produced, we used a bioinformatics approach to identify and functionally express a UDP-D-glucuronate 4-epimerase (GAE1) from Arabidopsis. GAE1 is predicted to be a type II membrane protein that belongs to the family of short-chain dehydrogenases/reductases. The recombinant enzyme expressed in Pichia pastoris established a 1.3:1 equilibrium between UDP-D-galacturonate and UDP-D-glucuronate but did not epimerize UDP-D-Glc or UDP-D-Xyl. Enzyme assays on cell extracts localized total UDP-D-glucuronate 4-epimerase and recombinant GAE1 activity exclusively to the microsomal fractions of Arabidopsis and Pichia, respectively. GAE1 had a pH optimum of 7.6 and an apparent Km of 0.19 mm. The recombinant enzyme was strongly inhibited by UDP-D-Xyl but not by UDP, UDP-D-Glc, or UDP-D-Gal. Analysis of Arabidopsis plants transformed with a GAE1:GUS construct showed expression in all tissues. The Arabidopsis genome contains five GAE1 paralogs, all of which are transcribed and predicted to contain a membrane anchor. This suggests that all of these enzymes are targeted to an endomembrane system such as the Golgi where they may provide UDP-D-galacturonate to glycosyltransferases in pectin synthesis.     

Enzymes of serine and glycine metabolism in leaves and non-photosynthetic tissues of Pisum sativum L.

A comparative study is presented of the activities of enzymes of glycine and serine metabolism in leaves, germinated cotyledons and root apices of pea (Pisum sativum L.). Data are given for aminotransferase activities with glyoxylate, hydroxypyruvate and pyruvate, for enzymes associated with serine synthesis from 3-phosphoglycerate and for glycine decarboxylase and serine hydroxymethyltransferase. Aminotransferase activities differ between the tissues in that, firstly, appreciable transamination of serine, hydroxypyruvate and asparagine occurs only in leaf extracts and, secondly, glyoxylate is transaminated more actively than pyruvate in leaf extracts, whereas the converse is true of extracts of cotyledons and root apices. Alanine is the most active amino-group donor to both glyoxylate and hydroxypyruvate. 3-Phosphoglycerate dehydrogenase and glutamate: O-phosphohydroxypyruvate aminotransferase have comparable activities in all three tissues, except germinated cotyledons, in which the aminotransferase appears to be undetectable. Glycollate oxidase is virtually undetectable in the non-photosynthetic tissues and in these tissues the activity of glycerate dehydrogenase is much lower than that of 3-phosphoglycerate dehydrogenase. Glycine decarboxylase activity in leaves, measured in the presence of oxaloacetate, is equal to about 30–40% of the measured rate of CO₂ fixation and is therefore adequate to account for the expected rate of photorespiration. The activity of glycine decarboxylase in the non-photosynthetic tissues is calculated to be about 2–5% of the activity in leaves and has the characteristics of a pyridoxal-and tetrahydrofolate-dependent mitochondrial reaction; it is stimulated by oxaloacetate, although not by ADP. In leaves, the measured activity of serine hydroxymethyltransferase is somewhat lower than that of glycine decarboxylase, whereas in root apices it is substantially higher. Differential centrifugation of extracts of root apices suggests that an appreciable proportion of serine hydroxymethyltransferase activity is associated with the plastids.Abbreviation GOGAT l-Glutamine:2-oxoglutarate aminotransferase     

Shikimate pathway activity in shake and fermenter cultures of Cinchona succirubra

Cell suspension cultures of Cinchona succirubra were cultivated in shake cultures and for the first time in airlift fermenters. Under both conditions L-tryptophan exerts a stimulatory effect on alkaloid formation. In this context the regulatory pattern of some shikimate pathway enzymes was investigated in non-supplemented and tryptophan supplemented Cinchona cell cultures. A remarkable increase of tryptophan decarboxylase (TDC) activity was observed in Cinchona cells under the influence of tryptophan. Apparently, like in some other indole alkaloid producing cell cultures, a high TDC activity is a prerequisite for alkaloid formation. Growth pattern and some enzyme activities of C. succirubra fermenter cultures at controlled and non-regulated pH levels were followed. Optimum growth and alkaloid formation were recorded under non-regulated (normal) pH conditions.Abbreviations TDC tryptophan decarboxylase - try L-tyrosine - phe L-phenylalanine - DAHP 3-deoxy-D-arabino-heptulosonic acid-7-phosphate - trp L-tryptophan - E-4-P erythrose-4-phosphate - PEP phosphoenolpyruvate - MDH malate dehydrogenase - G-6-PDH glucose-6-phosphate dehydrogenase - 6-PG-DH 6-phosphogluconate dehydrogenase - Ch-mutase chorismate mutase - AS-synthase anthranilate synthase - n.d. not determined