Fractionation of cassava pectins and their detailed structural analyses using various pectinolytic enzymes.

In this study, we analyzed the pectin structure within the pulp of cassava. Cassava pectin, derived from cassava pulp treatment at 120 °C for 90 min, was separated into four fractions (CP-P, CP-SD1, CP-SD2F, and CP-SD2R) based on variations in water solubility, electrical properties, and molecular weights. Sugar composition analysis demonstrated an abundance of homogalacturonan (HG) in CP-P and CP-SD2F, rhamnogalacturonan I (RG-I) in CP-SD2R, and neutral sugars in CP-SD1. Because RG-I possesses a complex structure, we analyzed CP-SD2R using various pectinolytic enzymes. Galactose was the major sugar in CP-SD2R accounting for 49 %, of which 65 % originated from arabinogalactan I, 9 % from galactose and galactooligosaccharides, 5 % from arabinogalactan II, and 11 % from galactoarabinan. Seventy-four percent of arabinose in CP-SD2R was present as galactoarabinan. The methylation (DM) and acetylation (DAc) degrees of cassava pectin were 11 and 15 %, respectively. The HG and RG-I regions exhibited DAc values of 5 and 44 %, respectively, signifying the high DAc of RG-I compared to HG. Information derived from the structural analysis of cassava pectin will enable efficient degradation of pectin and cellulose, leading to the use of cassava pulp as a raw material for biorefineries.

Understanding wax ester synthesis in Euglena gracilis: Insights into mitochondrial anaerobic respiration.

Euglena gracilis, photosynthetic protist, has a unique ability to generate wax esters in the absence of oxygen, employing a distinctive fatty acid synthesis mechanism. Through comprehensive inhibitor assays and gene-silencing techniques, our research clearly emphasized the indispensable role of the mitochondrial anaerobic respiratory chain in this biosynthesis. We identified acyl-CoA dehydrogenase, electron transfer flavoprotein (ETF), and rhodoquinone (RQ) as central molecular components in the pathway. These findings strongly indicated a potential reversal of beta-oxidation occurring within mitochondria for fatty acid production in anaerobic conditions. Furthermore, our analysis revealed the pivotal function of nicotinamide nucleotide transhydrogenase (NNT) in efficiently managing the NADPH/NAD+ conversion essential for sustaining anaerobic metabolism. This review outlines our key findings and provides a comprehensive understanding of the molecular mechanisms that enable E. gracilis to produce wax ester anaerobically.

Horizontally Acquired Nitrate Reductase Realized Kleptoplastic Photoautotrophy of Rapaza viridis.

While photoautotrophic organisms utilize inorganic nitrogen as the nitrogen source, heterotrophic organisms utilize organic nitrogen and thus do not generally have an inorganic nitrogen assimilation pathway. Here, we focused on the nitrogen metabolism of Rapaza viridis, a unicellular eukaryote exhibiting kleptoplasty. Although belonging to the lineage of essentially heterotrophic flagellates, R. viridis exploits the photosynthetic products of the kleptoplasts and was therefore suspected to potentially utilize inorganic nitrogen. From the transcriptome data of R. viridis, we identified gene RvNaRL, which had sequence similarity to genes encoding nitrate reductases in plants. Phylogenetic analysis revealed that RvNaRL was acquired by a horizontal gene transfer event. To verify the function of the protein product RvNaRL, we established RNAi-mediated knock-down and CRISPR-Cas9-mediated knock-out experiments for the first time in R. viridis and applied them to this gene. The RvNaRL knock-down and knock-out cells exhibited significant growth only when ammonium was supplied. However, in contrast to the wild-type cells, no substantial growth was observed when nitrate was supplied. Such arrested growth in the absence of ammonium was attributed to impaired amino acid synthesis due to the deficiency of nitrogen supply from the nitrate assimilation pathway; this in turn resulted in the accumulation of excess photosynthetic products in the form of cytosolic polysaccharide grains, as observed. These results indicate that RvNaRL is certainly involved in nitrate assimilation by R. viridis. Thus, we inferred that R. viridis achieved its advanced kleptoplasty for photoautotrophy, owing to the acquisition of nitrate assimilation via horizontal gene transfer.

Euglena International Network (EIN): Driving euglenoid biotechnology for the benefit of a challenged world.

Euglenoids (Euglenida) are unicellular flagellates possessing exceptionally wide geographical and ecological distribution. Euglenoids combine a biotechnological potential with a unique position in the eukaryotic tree of life. In large part these microbes owe this success to diverse genetics including secondary endosymbiosis and likely additional sources of genes. Multiple euglenoid species have translational applications and show great promise in production of biofuels, nutraceuticals, bioremediation, cancer treatments and more exotically as robotics design simulators. An absence of reference genomes currently limits these applications, including development of efficient tools for identification of critical factors in regulation, growth or optimization of metabolic pathways. The Euglena International Network (EIN) seeks to provide a forum to overcome these challenges. EIN has agreed specific goals, mobilized scientists, established a clear roadmap (Grand Challenges), connected academic and industry stakeholders and is currently formulating policy and partnership principles to propel these efforts in a coordinated and efficient manner.

Gelation of konjac glucomannan by acetylmannan esterases from Aspergillus oryzae.

Konjac glucomannan (KGM) is a principal component of the gelatinous food Konjac. Konjac production through alkali treatment releases an undesirable amine-odor. Two acetylesterases (AME1 and AME2) active against konjac glucomannan (polymer or oligomer) were purified from the supernatant of Aspergillus oryzae RIB40 culture. We cloned the genes encoding AME1 and AME2 based on the genomic information of A. oryzae, constructed their expression systems in A. oryzae, and obtained the recombinant enzymes (rAME1 and rAME2). rAME1 did not act on the KGM polymer but only on the KGM oligomer, releasing approximately 60% of the acetic acid in the substrate. However, rAME2 was active against both KGM substrates, releasing approximately 80% and 100% of acetic acid from the polymer and oligomer, respectively. Both enzymes were active against xylan and exhibited a trace activity on ethyl ferulate. The acetyl group position specificities of both enzymes were analyzed via heteronuclear single quantum correlation NMR using oligosaccharides of glucomannan prepared from Aloe vera (AGM), which has a higher acetyl group content than KGM. rAME1 acted specifically on single-substituted acetyl groups and not on double-substituted ones. In contrast, rAME2 appeared to act on all the acetyl groups in AGM. Treatment of 3% KGM with rAME2 followed by heating to 90 °C resulted in gel formation under weakly acidic conditions. This is the first study to induce gelation of KGM under these conditions. A comparison of the breaking and brittleness properties of gels formed by alkaline and enzymatic treatments revealed similar texture of the two gels. Furthermore, scanning electron microscopy of the surface structure of both gels revealed that both formed a fine mesh structure. Our findings on enzymatic gelation of KGM should lead to the development of new applications in food manufacturing industry.

Post-marketing surveillance of the safety and effectiveness of naldemedine in the management of opioid-induced constipation in patients with cancer pain in Japan.

PURPOSE: This prospective post-marketing surveillance (PMS) was designed to collect data on the safety and effectiveness of naldemedine in routine clinical practice in patients with opioid-induced constipation (OIC) and cancer pain in Japan and explore the characteristics of patients prone to diarrhea. METHODS: The enrolled patients received naldemedine (0.2 mg, once a day) orally for up to 12 weeks. In the safety analysis, adverse drug reactions (ADRs), including diarrhea as a special interest, were assessed. Effectiveness was evaluated, especially regarding the frequency and condition of bowel movement. RESULTS: In the safety analysis set (n = 1177), 145 ADRs occurred in 133 (11.30%) patients, and diarrhea was the most frequent event (n = 107, 9.09%). Most cases of diarrhea were non-serious (98.1%). Most ADRs were non-serious (93.8%), and they resolved within 2 weeks (75.9%). No patient characteristics influenced the risk of diarrhea development or aggravation. Both the frequency (75.0% and 83.2%) and condition of bowel movement (80.0% and 88.0%) were improved at 2 and 12 weeks, respectively in the effectiveness analysis set (n = 953). Frequency and condition of bowel movement were also improved in patients excluded (e.g., Eastern Cooperative Oncology Group performance status was ≥ 3) or with very small numbers (e.g., received weak opioid) in the clinical trials. CONCLUSIONS: This PMS indicates that naldemedine is well tolerated and effective in patients of various backgrounds in routine clinical practice who have OIC and cancer pain. TRIAL REGISTRATION: UMIN000042851.

Novel acid trehalase belonging to glycoside hydrolase family 37 from Pleurotus sp.: cloning, expression and characterization.

The N-terminal amino acid sequence of the Pleurotus sp. 90 kDa protein was in good agreement with the corresponding sequence of the glycoside hydrolase (GH) family 37 protein (trehalase) from P. ostreatus PC 15 v2.0. The length of the Pleurotus sp. trehalase gene was 2247 bp, encoding a protein of 749 amino acids with a predicted molecular mass of 81.2 kDa. The molecular mass of the recombinant enzyme was estimated to be about 117 kDa by SDS-PAGE. We found that the recombinant enzyme comprised an N-glycosylated sugar chain and that its optimum pH and temperature were 4.5 and 40 ºC, respectively. Moreover, this enzyme exhibited high activity against trehalose exclusively. We found that the enzyme is novel acid trehalase belonging to GH family 37.

NADPH-to-NADH conversion by mitochondrial transhydrogenase is indispensable for sustaining anaerobic metabolism in Euglena gracilis.

Euglena gracilis produces ATP in the anaerobic mitochondria with concomitant wax ester formation, and NADH is essential for ATP formation and fatty acid synthesis in the mitochondria. This study demonstrated that mitochondrial cofactor conversion by nicotinamide nucleotide transhydrogenase (NNT), converting NADPH/NAD+ to NADP+ /NADH, is indispensable for sustaining anaerobic metabolism. Silencing of NNT genes significantly decreased wax ester production and cellular viability during anaerobiosis but had no such marked effects under aerobic conditions. An analogous phenotype was observed in the silencing of the gene encoding a mitochondrial NADP+ -dependent malic enzyme. These results suggest that the reducing equivalents produced in glycolysis are shuttled to the mitochondria as malate, where cytosolic NAD+ regeneration is coupled with mitochondrial NADPH generation.

Novel cold-adapted raw-starch digesting α-amylases from Eisenia fetida: Gene cloning, expression, and characterization.

We identified the raw-starch-digesting α-amylase genes a earthworm Eisenia fetid α amylase I and II (Ef-Amy I and Ef-Amy II). Each gene consists of 1,530 base pairs (bp) that encode proteins of 510 amino acids, as indicated by the corresponding mRNA sequences. Ef-Amy I and II showed an 89% amino acid identity. The amino acid sequences of Ef-Amy I and II were similar to those of the α-amylases from porcine pancreas, human pancreas, Tenebrio molitor, Oryctolagus cuniculus, and Xenopus (Silurana) tropicalis. Each gene encoding mature Ef-Amy I and II was expressed in the GS115 strain of Pichia pastoris. The molecular masses of the recombinant Ef-Amy I and II were 57 kDa each, and catalytically important residues of α-amylases of the GH family 13 were conserved in both proteins. These amylases exhibited raw-starch-digesting activity at 4 °C. The substrate specificities of rEf-Amy I and II were dissimilar. rEf-Amy I and II were shown to be active even in 40% ethanol, 4 M NaCl, and 4 M KCl.

Homogalacturonan and xylogalacturonan region specificity of self-cloning vector-expressed pectin methylesterases (AoPME1-3) in Aspergillus oryzae.

Aspergillus oryzae is a safe microorganism that is commonly used in food production. We constructed a self-cloning vector capable of high expression in A. oryzae. Using the vector, three putative pectin methylesterase (PME) genes belonging to Carbohydrate Esterase family 8 derived from A. oryzae were expressed, and several characteristics of the gene products were examined. The effects of temperature and pH on the three enzymes (AoPME1, 2, and 3) were similar, with optimal reaction temperatures of 50 - 60 °C and optimal reaction pH range of 5 - 6. The specific activities of AoPME1, 2, and 3 for apple pectin were significantly different (34, 7,601, and 2 U/mg, respectively). When the substrate specificity was examined, AoPME1 showed high activity towards pectin derived from soybean and pea. Although AoPME2 showed little activity towards these pectins, it showed very high activity towards apple- and citrus-derived pectins. AoPME3 showed low specific activity towards all substrates tested. Sugar composition analysis revealed that apple- and citrus-derived pectins were rich in homogalacturonan, while soybean- and pea-derived pectins were rich in xylogalacturonan. When pea pectin was treated with endo-polygalacturonase or endo-xylogalacturonase in the presence of each PME, specific synergistic actions were observed (endo-polygalacturonase with AoPME1 or AoPME2 and endo-xylogalacturonase with AoPME1 or AoPME3). Thus, AoPME1 and AoPME3 hydrolyzed the methoxy group in xylogalacturonan. This is the first report of this activity in microbial enzymes. Our findings on the substrate specificity of PMEs should lead to the determination of the distribution of methoxy groups in pectin and the development of new applications in the field of food manufacturing.

Safety and effectiveness of baloxavir marboxil for the treatment of influenza in Japanese clinical practice: A postmarketing surveillance of more than 3000 patients.

Baloxavir marboxil is an oral anti-influenza drug that inhibits the cap-dependent endonuclease of the virus polymerase acidic protein. In clinical trials, baloxavir reduced the time to alleviation of influenza symptoms and time to resolution of fever in adults, adolescents, and children. The purpose of this study is to collect data on the safety and effectiveness of baloxavir when used in clinical practice. This postmarketing surveillance (clinicaltrials.jp; JapicCTI-183882), conducted at 688 Japanese hospitals or clinics (March 2018 to March 2019), enrolled patients of any age with influenza A or B infection who received a single, weight-based dose of baloxavir. Adverse drug reactions (ADRs) were seen in 11.2% of 3094 patients during the 7-day observation period; the most common ADR was diarrhea (6.1%). ADRs were more common in children aged <12 years (14.1%) than in adults (10.0%). Almost all ADRs were non-serious (98.9%) and were recovered or recovering (96.7%). Median time to alleviation of symptoms (N = 2884) was 2.5 days (overall, influenza A, and influenza B groups). Median time to resolution of fever (N = 2946) was 1.5 days (overall, influenza A, and influenza B groups). Biphasic fever (increased temperature after previous fever resolution) was seen in 6.7% of patients overall and 28.6% of patients <6 years infected with influenza B, similar to rates published elsewhere with other influenza drugs and in untreated influenza. This postmarketing surveillance of >3000 patients suggests that baloxavir is well tolerated and effective regardless of patient age or influenza virus type.

Determination of chemical structure of pea pectin by using pectinolytic enzymes.

The chemical structure of pea pectin was delineated using pectin-degrading enzymes and biochemical methods. The molecular weight of the pea pectin preparation was 488,000, with 50 % arabinose content, and neutral sugar side chains attached to approximately 60 % of the rhamnose residues in rhamnogalacturonan-I (RG-I). Arabinan, an RG-I side chain, was highly branched, and the main chain was comprised of α-1,5-l-arabinan. Galactose and galactooligosaccharides were attached to approximately 35 % of the rhamnose residues in RG-I. Long chain ß-1,4-galactan was also present. The xylose substitution rate in xylogalacturonan (XGA) was 63 %. The molar ratio of RG-I/homogalacturonan (HG)/XGA in the backbone of the pea pectin was approximately 3:3:4. When considering neutral sugar side chain content (arabinose, galactose, and xylose), the molar ratio of RG-I/HG/XGA regions in the pea pectin was 7:1:2. These data will help understand the properties of pea pectin.

Characterization of three GH35 ß-galactosidases, enzymes able to shave galactosyl residues linked to rhamnogalacturonan in pectin, from Penicillium chrysogenum 31B.

Three recombinant ß-galactosidases (BGALs; PcBGAL35A, PcBGAL35B, and PcGALX35C) belonging to the glycoside hydrolase (GH) family 35 derived from Penicillium chrysogenum 31B were expressed using Pichia pastoris and characterized. PcBGAL35A showed a unique substrate specificity that has not been reported so far. Based on the results of enzymological tests and 1H-nuclear magnetic resonance, PcBGAL35A was found to hydrolyze ß-1,4-galactosyl residues linked to L-rhamnose in rhamnogalacturonan-I (RG-I) of pectin, as well as p-nitrophenyl-ß-D-galactopyranoside and ß-D-galactosyl oligosaccharides. PcBGAL35B was determined to be a common BGAL through molecular phylogenetic tree and substrate specificity analysis. PcGALX35C was found to have similar catalytic capacities for the ß-1,4-galactosyl oligomer and polymer. Furthermore, PcGALX35C hydrolyzed RG-I-linked ß-1,4-galactosyl oligosaccharide side chains with a degree of polymerization of 2 or higher in pectin. The amino acid sequence similarity of PcBGAL35A was approximately 30% with most GH35 BGALs, whose enzymatic properties have been characterized. The amino acid sequence of PcBGAL35B was approximately 80% identical to those of BGALs from Penicillium sp. The amino acid sequence of PcGALX35C was classified into the same phylogenetic group as PcBGAL35A. Pfam analysis revealed that the three BGALs had five domains including a catalytic domain. Our findings suggest that PcBGAL35A and PcGALX35C are enzymes involved in the degradation of galactosylated RG-I in pectin. The enzymes characterized in this study may be applied for products that require pectin processing and for the structural analysis of pectin.

Taming chlorophylls by early eukaryotes underpinned algal interactions and the diversification of the eukaryotes on the oxygenated Earth.

Extant eukaryote ecology is primarily sustained by oxygenic photosynthesis, in which chlorophylls play essential roles. The exceptional photosensitivity of chlorophylls allows them to harvest solar energy for photosynthesis, but on the other hand, they also generate cytotoxic reactive oxygen species. A risk of such phototoxicity of the chlorophyll must become particularly prominent upon dynamic cellular interactions that potentially disrupt the mechanisms that are designed to quench photoexcited chlorophylls in the phototrophic cells. Extensive examination of a wide variety of phagotrophic, parasitic, and phototrophic microeukaryotes demonstrates that a catabolic process that converts chlorophylls into nonphotosensitive 132,173-cyclopheophorbide enols (CPEs) is phylogenetically ubiquitous among extant eukaryotes. The accumulation of CPEs is identified in phagotrophic algivores belonging to virtually all major eukaryotic assemblages with the exception of Archaeplastida, in which no algivorous species have been reported. In addition, accumulation of CPEs is revealed to be common among phototrophic microeukaryotes (i.e., microalgae) along with dismantling of their secondary chloroplasts. Thus, we infer that CPE-accumulating chlorophyll catabolism (CACC) primarily evolved among algivorous microeukaryotes to detoxify chlorophylls in an early stage of their evolution. Subsequently, it also underpinned photosynthetic endosymbiosis by securing close interactions with photosynthetic machinery containing abundant chlorophylls, which led to the acquisition of secondary chloroplasts. Our results strongly suggest that CACC, which allowed the consumption of oxygenic primary producers, ultimately permitted the successful radiation of the eukaryotes throughout and after the late Proterozoic global oxygenation.

Anaerobic respiration coupled with mitochondrial fatty acid synthesis in wax ester fermentation by Euglena gracilis.

In Euglena gracilis, wax ester fermentation produces ATP during anaerobiosis. Here, we report that anaerobic wax ester production is suppressed when the mitochondrial electron transport chain complex I is inhibited by rotenone, whereas it is increased by the uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP). The ADP/ATP ratio in anaerobic cells is elevated by treatment with either rotenone or CCCP. Gene silencing experiments indicate that acyl-CoA dehydrogenase, electron transfer flavoprotein (ETF), and rhodoquinone (RQ) participate in wax ester production. These results suggest that fatty acids are synthesized in mitochondria by the reversal of ß-oxidation, where trans-2-enoyl-CoA is reduced mainly by acyl-CoA dehydrogenase using the electrons provided by NADH via the electron transport chain complex I, RQ, and ETF, and that ATP production is highly supported by anaerobic respiration utilizing trans-2-enoyl-CoA as a terminal electron acceptor.

Gene cloning, expression, and X-ray crystallographic analysis of a ß-mannanase from Eisenia fetida.

The endo-1,4-ß-mannanases (Ef-Man) gene from Eisenia fetida was determined to consist of 1131 bp and encode a 377 amino acid protein. The amino acid sequence showed similarity with the endo-1,4-ß-mannanases of Daphnia pulex (62%), Cryptopygus antarcticus (64%), Crassostrea gigas (61%), Mytilus edulis (60%), and Aplysia kurodai (58%). The gene encoding mature Ef-Man was expressed in Pichia pastoris (GS115 strain). Based on SDS-PAGE analysis, the molecular mass of the purified recombinant Ef-Man (rEf-Man) was estimated to be 39 kDa. All catalytically important residues of endo-1,4-ß-mannanases in the glycoside hydrolase (GH) family 5 were conserved in Ef-Man. The optimal temperature for rEf-Man was identified as 60 °C. HPLC and HPAEC analyses suggest that Ef-Man requires at least six subsites for efficient hydrolysis and is capable of performing transglycosylation reactions. The overall structure of rEf-Man is similar to those of GH5 family proteins, and tertiary structures around the active site are conserved among endo-1,4-ß-mannanase families. X-ray crystallographic analysis supports the hydrolysis and transglycosylation reaction mechanism determined by HPLC and HPAEC analyses.

Crystal structure of exo-rhamnogalacturonan lyase from Penicillium chrysogenum as a member of polysaccharide lyase family 26.

Exo-rhamnogalacturonan lyase from Penicillium chrysogenum 31B (PcRGLX) was recently classified as a member of polysaccharide lyase (PL) family 26 along with hypothetical proteins derived from various organisms. In this study, we determined the crystal structure of PcRGLX as the first structure of a member of this family. Based on the substrate-binding orientation and substrate specificity, PcRGLX is an exo-type PL that cleaves rhamnogalacturonan from the reducing end. Analysis of PcRGLX-complex structures with reaction products indicate that the active site possesses an L-shaped cleft that can accommodate galactosyl side chains, suggesting side-chain-bypassing activity in PcRGLX. Furthermore, we determined the residues critical for catalysis by analyzing the enzyme activities of inactive variants.

Physiological functions of pyruvate:NADP+ oxidoreductase and 2-oxoglutarate decarboxylase in Euglena gracilis under aerobic and anaerobic conditions.

In Euglena gracilis, pyruvate:NADP+ oxidoreductase, in addition to the pyruvate dehydrogenase complex, functions for the oxidative decarboxylation of pyruvate in the mitochondria. Furthermore, the 2-oxoglutarate dehydrogenase complex is absent, and instead 2-oxoglutarate decarboxylase is found in the mitochondria. To elucidate the central carbon and energy metabolisms in Euglena under aerobic and anaerobic conditions, physiological significances of these enzymes involved in 2-oxoacid metabolism were examined by gene silencing experiments. The pyruvate dehydrogenase complex was indispensable for aerobic cell growth in a glucose medium, although its activity was less than 1% of that of pyruvate:NADP+ oxidoreductase. In contrast, pyruvate:NADP+ oxidoreductase was only involved in the anaerobic energy metabolism (wax ester fermentation). Aerobic cell growth was almost completely suppressed when the 2-oxoglutarate decarboxylase gene was silenced, suggesting that the tricarboxylic acid cycle is modified in Euglena and 2-oxoglutarate decarboxylase takes the place of the 2-oxoglutarate dehydrogenase complex in the aerobic respiratory metabolism.

A novel α-galactosidase from Fusarium oxysporum and its application in determining the structure of the gum arabic side chain.

We previously reported that Fusarium oxysporum 12S produces two bifunctional proteins, FoAP1 and FoAP2, with α-d-galactopyranosidase (GPase) and ß-l-arabinopyranosidase (APase) activities. The aim of this paper was to purify a third GPase, FoGP1, from culture supernatant of F. oxysporum 12S, to characterize it, and to determine its mode of action towards gum arabic. A cDNA encoding FoGP1 was cloned and the protein was overexpressed in Escherichia coli. Module sequence analysis revealed the presence of a GH27 domain in FoGP1. The recombinant enzyme (rFoGP1) showed a GPase/APase activity ratio of 330, which was quite different from that of FoAP1 (1.7) and FoAP2 (0.2). Among the natural substrates tested, rFoGP1 showed the highest activity towards gum arabic. In contrast to other well-characterized GPases, rFoGP1 released a small amount of galactose from α-galactosyl oligosaccharides such as raffinose and exhibited no activity toward galactomannans, which are highly substituted with α-galactosyl side chains. This indicated that FoGP1 is an unusual type of GPase. rFoGP1 released 30% of the total galactose from gum arabic, suggesting the existence of a large number of α-galactosyl residues at the non-reducing ends of gum arabic side chains. Together, rFoGP1 and α-l-arabinofuranosidase released four times more arabinose than α-l-arabinofuranosidase acting alone. This suggested that a large number of α-l-arabinofuranosyl residues is capped by α-galactosyl residues. 1H NMR experiments revealed that rFoGP1 hydrolyzed the α-1,3-galactosidic linkage within the side chain structure of [α-d-Galp-(1→3)-α-l-Araf-(1→] in gum arabic. In conclusion, rFoGP1 is highly active toward α-1,3-galactosyl linkages but negligibly or not active toward α-1,6-galactosyl linkages. The novel FoGP1 might be used to modify the physical properties of gum arabic, which is an industrially important polysaccharide used as an emulsion stabilizer and coating agent.

C2 metabolism in Euglena.

Euglenoids are able to assimilate fatty acids and alcohols with various carbon-chain lengths, and ethanol is known to be one of the best carbon sources to support the growth of Euglena gracilis. Ethanol is first oxidized to acetate by the sequential reactions of alcohol dehydrogenase and acetaldehyde dehydrogenase in the mitochondria, and then converted to acetyl coenzyme A (acetyl-CoA). Acetyl-CoA is metabolized through the glyoxylate cycle which is a modified tricarboxylic acid (TCA) cycle in which isocitrate lyase (ICL) and malate synthase (MS) function to bypass the two decarboxylation steps of the TCA cycle, enabling the net synthesis of carbohydrates from C2 compounds. ICL and MS form a unique bifunctional enzyme localized in Euglena mitochondria, not in glyoxysome as in other eukaryotes. The unique glyoxylate and glycolate metabolism during photorespiration is also discussed in this chapter.