Measurement of the content of limit-dextrinase in cereal flours.
McCleary, B. V. (1992). Carbohydrate Research, 227, 257-268.
Procedures for the quantitative extraction, activation, and assay of limit-dextrinase in cereal flours have been developed. Extraction and activation require incubation in buffer containing 20mm cysteine for at least 16 h or with 25mM dithiothreitol for 5 h. Activity is assayed with a soluble, dyed substrate (Red-Pullulan) or an insoluble, dyed, and cross-linked substrate (Azurine-CL-Pullulan) which is dispensed in tablet form (Limit-DextriZyme tablets).
Overexpression of thioredoxin h leads to enhanced activity of starch debranching enzyme (pullulanase) in barley grain.
Cho, M. J., Wong, J. H., Marx, C., Jiang, W., Lemaux, P. G. & Buchanan, B. B. (1999). Proceedings of the National Academy of Sciences, 96(25), 14641-14646.
Biochemically active wheat thioredoxin h has been overexpressed in the endosperm of transgenic barley grain. Two DNA constructs containing the wheat thioredoxin h gene (wtrxh) were used for transformation; each contained wtrxh fused to an endosperm-specific B1-hordein promoter either with or without a signal peptide sequence for targeting to the protein body. Twenty-two stable, independently transformed regenerable lines were obtained by selecting with the herbicide bialaphos to test for the presence of the barherbicide resistance gene on a cotransformed plasmid; all were positive for this gene. The presence of wtrxh was confirmed in 20 lines by PCR analysis, and the identity and level of expression of wheat thioredoxin h was assessed by immunoblots. Although levels varied among the different transgenic events, wheat thioredoxin h was consistently highly expressed (up to 30-fold) in the transgenic grain. Transgenic lines transformed with the B1-hordein promoter with a signal peptide sequence produced a higher level of wheat thioredoxin h on average than those without a signal sequence. The overexpression of thioredoxin h in the endosperm of germinated grain effected up to a 4-fold increase in the activity of the starch debranching enzyme, pullulanase (limit dextrinase), the enzyme that specifically cleaves α-1,6 linkages in starch. These results raise the question of how thioredoxin h enhances the activity of pullulanase because it was found that the inhibitor had become inactive before the enzyme showed appreciable activity.
A starch‐accumulating mutant of Arabidopsis thaliana deficient in a chloroplastic starch‐hydrolysing enzyme.
Zeeman, S. C., Northrop, F., Smith, A. M. & Rees, T. A. (1998). The Plant Journal, 15(3), 357-365.
The aim of this work was to identify enzymes that participate in the degradation of transitory starch in Arabidopsis. A mutant line was isolated by screening leaves at the end of the night for the presence of starch. The mutant had a higher starch content than the wild-type throughout the diurnal cycle. This accumulation was due to a reduction in starch breakdown, leading to an imbalance between the rates of synthesis and degradation. No reduction in the activity of endo-amylase (α-amylase), β-amylase, starch phosphorylase, maltase, pullulanase or D-enzyme could be detected in crude extracts of leaves of the mutant. However, native PAGE in gels containing amylopectin revealed that a starch-hydrolysing activity, putatively identified as an endo-amylase and present in wild-type chloroplasts, was absent or appreciably reduced in the mutant. This is the first time that a specific enzyme required for starch degradation has been identified in leaves.
The starch-debranching enzymes isoamylase and pullulanase are both involved in amylopectin biosynthesis in rice endosperm.
Kubo, A., Fujita, N., Harada, K., Matsuda, T., Satoh, H. & Nakamura, Y. (1999). Plant Physiology, 121(2), 399-410.
The activities of the two types of starch debranching enzymes, isoamylase and pullulanase, were greatly reduced in endosperms of allelic sugary-1 mutants of rice (Oryza sativa), with the decrease more pronounced for isoamylase than for pullulanase. However, the decrease in isoamylase activity was not related to the magnitude of the sugary phenotype (the proportion of the phytoglycogen region of the endosperm), as observed with pullulanase. In the moderately mutated line EM-5, the pullulanase activity was markedly lower in the phytoglycogen region than in the starch region, and isoamylase activity was extremely low or completely lost in the whole endosperm tissue. These results suggest that both debranching enzymes are involved in amylopectin biosynthesis in rice endosperm. We presume that isoamylase plays a predominant role in amylopectin synthesis, but pullulanase is also essential or can compensate for the role of isoamylase in the construction of the amylopectin multiple-cluster structure. It is highly possible that isoamylase was modified in some sugary-1 mutants such as EM-273 and EM-5, since it was present in significant and trace amounts, respectively, in these mutants but was apparently inactive. The results show that the Sugary-1 gene encodes the isoamylase gene of the rice genome.
Enzymatic properties and regulation of ZPU1, the maize pullulanase-type starch debranching enzyme.
Wu, C., Colleoni, C., Myers, A. M. & James, M. G. (2002). Archives of Biochemistry and Biophysics, 406(1), 21-32.
Starch debranching enzymes (DBE) are required for mobilization of carbohydrate reserves and for the normal structural organization of storage glucan polymers. Two isoforms, the pullulanase-type DBEs and the isoamylase-type DBEs, are both highly conserved in plants. To address DBE functions in starch assembly and breakdown, this study characterized the biochemical activity of ZPU1, a pullulanase-type DBE that is the product of the maize Zpu1 gene. Assays showed directly that recombinant ZPU1 (ZPU1r) expressed in Escherichia coli functions as a pullulanase-type enzyme, and 1H-NMR spectroscopy demonstrated that ZPU1r specifically hydrolyzes α-(1→6) branch linkages. Preferred substrates for ZPU1r hydrolytic activity were determined, as were pH, temperature, and thermal stability optima. Kinetic properties of ZPU1r with respect to two substrates, β-limit dextrin and pullulan, were determined. ZPU1 activity was increased by incubation with thioredoxin h, and native activity was decreased in mutants that accumulate soluble sugars, suggesting potential regulatory mechanisms.
The effect of storage temperature on reducing sugar concentration and the activities of three amylolytic enzymes in tubers of the cultivated potato, Solanum tuberosum L.
Cottrell, J. E., Duffus, C. M., Paterson, L., Mackay, G. R., Allison, M. J. & Bain, H. (1993). Potato Research, 36(2), 107-117.
Reducing sugar content, and activities of three starch hydrolysing enzymes, alpha-amylase, beta-amylase and debranching enzyme were measured over several months in tubers of five cultivars stored at 4°C or 10°C. Cultivars differed in their sensitivity to storage temperature. Reducing sugar content of tubers and the activities of three starch hydrolysing enzymes increased sharply during the first weeks of storage at 4°C. At 10°C, reducing sugar content, and the activity of the three enzymes remained constant or increased only slightly.
In vitro pullulanase activity of wheat (Triticum aestivum L.) limit-dextrinase type starch debranching enzyme is modulated by redox conditions.
Repellin, A., Båga, M. & Chibbar, R. N. (2008). Journal of Cereal Science, 47(2), 302-309.
Expression of a limit-dextrinase (LD) type starch debranching enzyme (EC 188.8.131.52) was observed in developing wheat (Triticum aestivum L.) endosperm and germinating grains, indicating a role for the enzyme in both biosynthesis and degradation of starch. A full-length cDNA, TaLD1, encoding LD in wheat developing kernels was isolated and predicted to encode a 98.6 kDa mature protein active in amyloplasts. Isolated cDNA was expressed in Escherichia coli to produce a recombinant His-tagged LD, which mainly accumulated in inclusion bodies as an inactive enzyme. Extraction of His-tagged LD from the inclusion bodies followed by dialysis under thiol/disulphide redox conditions allowed partial refolding of the protein and detection of pullulanase specific activities by zymogram analysis and enzyme assays. Several active conformations were demonstrated by the recombinant TaLD1 and pullulanase activity could be modulated by redox conditions in vitro. The results suggest that cellular redox conditions may regulate the level of LD activity in wheat tissues.
Flavobacterium frigidarium sp. nov., an aerobic, psychrophilic, xylanolytic and laminarinolytic bacterium from Antarctica.
Humphry, D. R., George, A., Black, G. W. & Cummings, S. P. (2001). International Journal of Systematic and Evolutionary Microbiology, 51(4), 1235-1243.
A psychrophilic, aerobic bacterium designated A2iT was isolated from marine sediment recovered from shallow waters surrounding Adelaide Island, Antarctica (67° 34' S, 68° 07' W). The organism exhibited xylanolytic and laminarinolytic activity and was halotolerant. Basic characterization showed that it was gram-negative, non-motile, yellow-pigmented (β, β-carotene-3,3'-diol) and positive for oxidase and catalase synthesis. Analysis of the 16S rDNA sequence suggests that the organism belongs to the Flexibacter-Cytophaga-Bacteroides phylum. On the basis of its 16S rDNA sequence, the bacterium is 96.8% similar to Flavobacterium columnare ATCC 43622 - its closest relation. The genomic DNA G+C content was 35 mol%. Growth on xylan occurs optimally at 15°C, though growth also occurs at 0°C, and the doubling times are 9.6 and 34.8 h, respectively. The maximum growth temperature on xylan is at 24°C. The bacterium is a neutrophile, growing across the pH range 5.6-8.4 and having an optimum at pH 7.5. Analysis of the 16S rDNA sequence, together with phenotypic characterization, suggests that the organism is a member of the genus Flavobacterium. DNA-DNA hybridization experiments have shown that it is a novel species; it is proposed, therefore, that the organism be designated as the type strain of Flavobacterium frigidarium sp. nov. (= ATCC 700810T = NCIMB 13737T).
Expression and secretion of Bacillus polymyxa neopullulanase in Saccharomyces cerevisiae.
Yebra, M. J., Blasco, A. & Sanz, P. (1999). FEMS Microbiology Letters, 170(1), 41-49.
We have isolated the gene encoding the neopullulanase enzyme from Bacillus polymyxa CECT 155. It consists of an open reading frame of 1545 bp that could code for a protein of 515 amino acids. This open reading frame was expressed in Bacillus subtilis and the corresponding transformants produced extracellular neopullulanase. The neopullulanase gene was also expressed in Saccharomyces cerevisiae placing it under the control of the yeast actin gene (ACT1) promoter. Clones containing the intact neopullulanase gene, including its own bacterial signal sequence, gave rise to the synthesis of active, but intracellular, enzyme by S.cerevisiae transformants. When sequences specifying the signal sequence and leader region of the yeast mating pheromone α-factor (MFα1) were fused upstream of the gene encoding the neopullulanase enzyme, the enzyme was secreted by S. cerevisiae. The secreted protein presented the same biochemical properties and the same apparent molecular mass as the Bacillus polymyxa original enzyme. The predicted amino acid sequence of the neopullulanase protein contained sequence motifs conserved among amylolytic enzymes. Northern blot analysis indicated that the transcription of the neopullulanase gene in B. polymyxa was induced by the presence of the substrate, pullulan, in the culture, and was repressed by glucose.
Protein heterogeneity of spinach pullulanase results from the coexistence of interconvertible isomeric forms of the monomeric enzyme.
Henker, A., Schindler, I., Renz, A. & Beck, E. (1998). Biochem. J, 331, 929-935.
Purified pullulanase (starch-debranching enzyme, R-enzyme, EC 184.108.40.206) from spinach (Spinacia oleracea L.) chloroplasts separated into at least seven individual enzymically active proteins (isomers, numbered 1–7) on isoelectric focusing or column chromatofocusing. At their isoelectric points (between pH 4.7 and 5.2) these forms were rather stable. At slightly alkaline pH, each converted into the whole set of isomers. PAGE of the purified enzyme under denaturing or non-denaturing conditions resulted in one protein band. When substrate (amylopectin or pullulan) was included in the gel, the native enzyme as well as any of the individual isomers separated into two (sometimes three) bands ('substrate-induced forms', numbered I–III) with different specific activities, dissociation constants of the enzyme–substrate complexes and activation energies. Each substrate-induced form produced the whole set of seven isomers on isoelectric focusing. The specific activity of the total enzyme reflected the relative proportions of the substrate-induced forms. To some extent the relative proportions, as determined by crossed immunoelectrophoresis, could be shifted in favour of the more or the less active forms by reduction with dithiothreitol, and gentle oxidation respectively. Activation by dithiothreitol did not alter the mode of action of the enzyme but only increased the velocity of substrate degradation and extended its activity into the pH range of the chloroplast. As a consequence of isomer interconversion, microheterogeneity could serve to regulate pullulanase activity in a biochemical manner that shares some features with allosteric regulation.
Characterization of novel neopullulanase from Bacillus polymyxa.
Yebra, M. J., Arroyo, J., Sanz, P. & Prieto, J. A. (1997). Applied Biochemistry and Biotechnology, 68(1), 113-120.
Bacillus polymyxa CECT 155 produces an extracellular neopullulanase activity that degrades pullulan to panose. This activity was stimulated by the presence of pullulan in the culture, and repressed by glucose. The apparent mol wt determined for the enzyme was 58 kDa. The optimum pH and temperature for neopullulanase activity were pH 6.0 and 50°C, respectively. The enzyme was stable in a pH range of 4.0–8.0, and temperatures up to 60°C. These properties make it suitable for the saccharification processes in the starch industries.