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.
Characterization of a type I pullulanase from Anoxybacillus sp. SK3-4 reveals an unusual substrate hydrolysis.
Kahar, U. M., Ng, C. L., Chan, K. G. & Goh, K. M. (2016). Applied Microbiology and Biotechnology, 100(14), 6291–6307.
Type I pullulanases are enzymes that specifically hydrolyse α-1,6 linkages in polysaccharides. This study reports the analyses of a novel type I pullulanase (PulASK) from Anoxybacillus sp. SK3-4. Purified PulASK (molecular mass of 80 kDa) was stable at pH 5.0-6.0 and was most active at pH 6.0. The optimum temperature for PulASK was 60°C, and the enzyme was reasonably stable at this temperature. Pullulan was the preferred substrate for PulASK, with 89.90 % adsorbance efficiency (various other starches, 56.26–72.93 % efficiency). Similar to other type I pullulanases, maltotriose was formed on digestion of pullulan by PulASK. PulASK also reacted with β-limit dextrin, a sugar rich in short branches, and formed maltotriose, maltotetraose and maltopentaose. Nevertheless, PulASK was found to preferably debranch long branches at α-1,6 glycosidic bonds of starch, producing amylose, linear or branched oligosaccharides, but was nonreactive against short branches; thus, no reducing sugars were detected. This is surprising as all currently known type I pullulanases produce reducing sugars (predominantly maltotriose) on digesting starch. The closest homologue of PulASK (95 % identity) is a type I pullulanase from Anoxybacillus sp. LM14-2 (Pul-LM14-2), which is capable of forming reducing sugars from starch. With rational design, amino acids 362-370 of PulASK were replaced with the corresponding sequence of Pul-LM14-2. The mutant enzyme formed reducing sugars on digesting starch. Thus, we identified a novel motif involved in substrate specificity in type I pullulanases. Our characterization may pave the way for the industrial application of this unique enzyme.
Purification and characterization of amylase from roots of Paederia foetida Linn.
Sottirattanapan, P., Nantachai, K., Daduang, S., Funahashi, T. & Yamada, M. (2017). Biocatalysis and Agricultural Biotechnology, 10, 329-335.
The root extract of Paederia foetida Linn. has been traditionally utilized for the improvement of taste and texture of various foods in Thailand. To identify a factor for the improvement, we performed biochemical analyses. Enzyme assay and zymographic method revealed that there is amylolytic activity in the root extract. This and SDS-polyacrylamide gel electrophoresis (PAGE) analyses suggest that an enzyme exhibiting amylolytic activity is a dominant protein in the extracts. By using DEAE-column chromatography, the amylase was purified to homogeneity, having a molecular mass on SDS-PAGE of 60 kDa. The purified enzyme showed pH- and temperature-optimum activities at 7.0 and at 50°C, respectively. The enzyme activity was found to be stable in the pH and temperature ranges of 6.0–7.5 and of 30–60°C, respectively, and was inhibited completely by the addition of Hg2+ and Cu2+ and partially by Fe3+.The amylase was active on starch>dextrin>amylopectin>glycogen>β-limit dextrin, but was inactive on pullulan and starch azure. HPLC analysis of starch hydrolysate by the enzyme showed maltose as a main product with no detectable glucose. The Km value for starch of the purified enzyme was determined to be 2.7±0.24 mg ml-1. Taken together, it is suggested that an enzyme responsible for amylolytic activity in the root extracts of Paederia foetida Linn. is β-amylase.
Effect of season, supplementation and fasting on glycolytic potential and activity of AMP-activated protein kinase, glycogen phosphorylase and glycogen debranching enzyme in grass-fed steers as determined in Longissimus lumborum muscle.
Apaoblaza, A., Strobel, P., Ramírez-Reveco, A., Jeréz-Timaure, N., Monti, G. & Gallo, C. (2017). Livestock Science, 202, 101-108.
Forty grass fed beef steers close to slaughter weight (500 kg) were used to study the effects of season (one experiment was carried out in autumn and one in summer, same farm, same design), supplementation (grass-fed only=control or flaked corn supplemented=suppl during four weeks before slaughter) and fasting during lairage (0 h or 24 h fasting). The supplementation with flaked corn started with 0.5 kg animal-1 day1, fed individually and increasing up to 1% of body weight (approximately 5 kg animal-1 day1) during the first week; this amount was kept constant for three more weeks. The concentrations of muscle glycogen (MGC), glucose-6-phosphate+glucose (G6P+Gluc) and lactate (LA), glycolytic potential (GPot), activity of AMP-activated protein kinase (AMPK), glycogen phosphorylase (GP) and glycogen debranching enzyme (GDE) were determined in M. Longissimus lumborum (LL);pH and postmortem temperature at 0.5 h and 24 h were measured. Biopsies from the LL were taken from each steer at the beginning of each experiment (B1), at 0.5 h (B2) and 24 h postmortem (B3). For each metabolic substrate/product measured in the muscle samples a linear mixed effect model was fitted. GPot, MGC and GP were higher and GDE was lower (P < 0.05) in autumn than in summer. Carcass temperature at 0.5 h and 24 h postmortem was lower in autumn than in summer and non-fasted steers had a lower final carcass temperature than those fasted (P < 0.05). Supplementation and no fasting were significant (P < 0.05) factors that helped maintaining a higher MGC and GPot in the steers between B1 (on farm biopsy) and B2 (at slaughter); no fasting also helped in increasing GDE activity postmortem (between B2 and B3).The effects of treatments on glycogen reserves and on the activities of the glycolytic enzymes included were not reflected in the ultimate pH of the carcasses, because no differences in terms of mean pH due to any of the factors studied were found (P > 0.05). Perhaps other substrates/enzymes that take part in muscle glycolysis/glycogenolysis not included in this study should be analyzed in future studies; considering the high individual variability observed, intrinsic factors of cattle, like genetics, should be taken into consideration.