In order to serve as a glycosyl donor, a sugar or a sugar derivative (e.g. GlcA) needs to be “activated” to a highly energetic state of a nucleotide-sugar. This activation requires the involvement of specific enzymes which produce NDP-sugars (or, in one case, NMP-sugar), using NTP or NDP as substrate. The present review provides concise survey of distinct plant nucleotide-sugar pyrophosphorylases (all using NTP as one of the substrates and differing in sugar specificity) as well as nucleotide-sugar phosphorylases and sucrose synthase (all using NDP as one of substrates). The pyrophosphorylases discussed include UGPase, USPase, UAGPase, AGPase, GMPase (VTC1), and FKGP, whereas phosphorylases include ADP-Glc phosphorylase and GDP-Gal phosphorylase (VTC2/VTC5). We also discuss the activation mechanism of 3-deoxy-D-manno-octulosonic acid (Kdo) by CKS, leading to the formation of a unique NMP-linked sugar (CMP-Kdo).
Glycogen is the predominant polysaccharide in living cells. Many microorganisms accumulate glycogen, which serves as an energy reserve to cope with harsh environmental conditions. Therefore, the functions of enzymes involved in glycogen synthesis and degradation must be deciphered to understand the survival mechanisms of microbes. However, these enzymes in bacteria, most of which are glycosyl transferases or glycosidases, have not been fully characterized. Although there are similarities, the processes of glycogen synthesis and degradation in bacteria are quite distinct from the same processes in eukaryotes. Considerable progress has been made in understanding the mode of glycogen metabolism in Escherichia coli. In addition to the common core pathway, the virulence factors of infecting enteropathogenic bacteria appear to be involved in glycogen degradation. This review will focus on the following: (i) enzymes involved in glycogen degradation in E. coli, (ii) comparisons of the glycogen enzymes within enterobacteria, and (iii) glycogen as a carbon source for infectious microbes.
1,2-β-Glucan was produced enzymatically from 1.0 M sucrose and 0.5 M glucose by the combination of sucrose phosphorylase and 1,2-β-oligoglucan phosphorylase in the presence of 100 mM inorganic phosphate. Accumulation of 1,2-β-glucan in 2 L of the reaction mixture reached over 800 mM (glucose equivalent). Sucrose, glucose and fructose were removed after the reaction by yeast treatment. 1,2-β-Glucan was precipitated with ethanol to obtain 167 g of 1,2-β-glucan from 1 L of the reaction mixture.
Diabetes is a lifestyle disease, and its prevention and treatment are extremely important. It is reported that inhibition of abrupt postprandial increase of glucose is effective to prevent the initiation of type 2 diabetes. We evaluated the efficacy of boiled rice soaked in MSTR (0.1% unsalted rice koji miso, 0.6% water-soluble extracts from ego seaweed, 5.6% water-soluble extracts from tomato, 5.6% water-soluble extracts from red onion, and 0.1% rice bran oil). Rice cultivars, including Japonica (Koshihikari) and ae mutants, (Hokurikukona243) were evaluated to assess the physical properties and chemical composition of the boiled rice grains. We investigated the inhibition of abrupt increases in postprandial blood glucose after consuming boiled rice using Sprague-Dawley rats. Blood glucose levels increase after consuming boiled rice soaked in MSTR were significantly lower than those of Koshihikari soaked in distilled water. The soaked boiled rice contained high levels of dietary fibers, glutamic acid, glucose content and a high 2, 2-dipheny1-1-picrylhydrazyl radical scavenging capacity. This treatment would improve the bio-functional properties of boiled rice. Furthermore, we developed formulae for estimating the postprandial blood glucose level based on the contents of resistant starch and glucose, and physical property (toughness) of boiled rice grains. It would lead to an easy method for selecting the palatable and bio-functional boiled rice.
Edible burdock (Arctium lappa L.) accumulates an inulin-type fructan. Inulin-type fructan in plant has been hydrolyzed by fructan 1-exohydrolases (1-FEH). We have previously reported on the cloning of aleh1, which encodes a 1-FEH in edible burdock. Here, we describe the cloning of aleh2, which encodes a 1-FEH isozyme in edible burdock, and the functional analysis of the recombinant protein of aleh2 (rAlEH2) that displays properties different from the aleh1 recombinant protein. A cDNA, named aleh2, was obtained by the RACE. The rAlEH2, which was produced by Pichia pastoris, showed 1-FEH activity. Unlike the recombinant protein of aleh1, the rAlEH2 is a 1-FEH enzyme that efficiently hydrolyzes longer-chain fructans than 1-kestose, such as nystose, fructosylnystose and inulin. The expression study in burdock revealed the induction of aleh1 and aleh2 genes by low temperature. These findings indicated that two 1-FEH isoforms were involved in the degradation of the fructan in burdock roots during low-temperature storage.
In this study, we extracted sago starch from sago pith waste (SPW) using a micro powder mill. The objectives were to recover the starch from the SPW and to understand the effects of micro powder milling on the physicochemical properties of micro-powder-milled sago starch. Milling was performed at different levels of disc clearance. Native sago starch extracted from sago pith, called untreated sago starch, was used as a comparison. The results show that micro powder milling of SPW can increase the sago starch yield by around 10‒17%, depending on the milling disc clearance. The amount of soluble starch in the SPW after micro powder milling was low for all treatments. The sago starch size distribution was wider at narrow clearance, but similar at wide, wide-medium, and medium-narrow clearances. Scanning electron microscopy showed that a narrow clearance treatment reduced the smoothness of the granule surface, and also reduced the starch granule birefringence. X-ray diffraction showed that the crystallinity decreased with decreasing milling clearance. Differential scanning calorimetry showed that the peak temperatures were similar at all levels, and the gelatinization enthalpy declined with decreasing crystallinity. The results suggest that sago starch can be recovered from SPW using micro powder milling, and the treatment, especially at narrow clearance, disrupts the crystalline regions of sago starch.
Starch is glucose polymer linked by α-1,4 and α-1,6 glucosidic bonds. The balance of activity between starch synthases (SSs) and branching enzymes (BEs) is important for formation of amylopectin structure. SSI and SSIIIa isozymes account for 60 and 30%, respectively, of soluble SS activity in developing rice endosperm. Complete loss of both SSI and SSIIIa activities induces sterility. By contrast, a double mutant (ss1L/ss3a) generated by crossing the leaky ss1 mutant, whose SS activity is approximately ca. 16% of the wild type, and the ss3a null mutant is fertile. Although there is only a significant residual SS activity in the developing endosperm of ss1L/ss3a, the yield and growth of the double-mutant line is sufficient. We analyzed the amylopectin chain-length distribution, thermal and pasting properties, morphologies of starch granules and amyloplasts, and crystallinity of endosperm starch in ss1L/ss3a and the parental mutant lines. The chain-length distribution pattern of ss1L/ss3a was similar to that of ss3a and there was an additive effect of the reduction of SSI activity on the chain-length of amylopectin in the ss3a background. These changes in the amylopectin chain-length distribution were considered to increase the gelatinization temperature of the starch. The gelatinized starch viscosity of the double-mutant and ss3a lines was very low. Most ss1L/ss3a starch granules were round-shaped, and the starch granular size was smaller than those of the parental mutant lines and the wild type. The starch crystallinity of ss1L/ss3a was slightly reduced compared with that of the wild type.
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