Criteria of choice of the helix type in crystalline dextran

Genin, Alexander; Banatskaya, M.I.; Nikitin, I V; Skokova, I. F.; Vainshtein, E.F.; Kushnerev, M.Ya.; Козлов, П.В.

doi:10.1016/0032-3950(83)90324-6

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“…The diameter of the iodine atom is 4.2 Å, as measured by Raman spectroscopy (33). The linear (1¡6)-␣-D-glucan model is based on the results of Genin et al (34), who showed that five glucose units per rotation in a right-handed helix is the most stable configuration. The inner diameter of such a helix is around 4.1 Å; therefore, the iodine anions cannot be trapped in the cavities of the (1¡6)-␣-D-glucan due to the steric hindrance.…”

Section: Figmentioning

confidence: 99%

Biochemical Characterization of the Lactobacillus reuteri Glycoside Hydrolase Family 70 GTFB Type of 4,6-α-Glucanotransferase Enzymes That Synthesize Soluble Dietary Starch Fibers

Bai

Kaaij

Leemhuis

et al. 2015

Appl Environ Microbiol

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c 4,6-␣-Glucanotransferase (4,6-␣-GTase) enzymes, such as GTFB and GTFW of Lactobacillus reuteri strains, constitute a new reaction specificity in glycoside hydrolase family 70 (GH70) and are novel enzymes that convert starch or starch hydrolysates into isomalto/maltopolysaccharides (IMMPs). These IMMPs still have linear chains with some ␣1¡4 linkages but mostly (relatively long) linear chains with ␣1¡6 linkages and are soluble dietary starch fibers. 4,6-␣-GTase enzymes and their products have significant potential for industrial applications. Here we report that an N-terminal truncation (amino acids 1 to 733) strongly enhances the soluble expression level of fully active GTFB-⌬N (approximately 75-fold compared to full-length wild type GTFB) in Escherichia coli. In addition, quantitative assays based on amylose V as the substrate are described; these assays allow accurate determination of both hydrolysis (minor) activity (glucose release, reducing power) and total activity (iodine staining) and calculation of the transferase (major) activity of these 4,6-␣-GTase enzymes. The data show that GTFB-⌬N is clearly less hydrolytic than GTFW, which is also supported by nuclear magnetic resonance (NMR) analysis of their final products. From these assays, the biochemical properties of GTFB-⌬N were characterized in detail, including determination of kinetic parameters and acceptor substrate specificity. The GTFB enzyme displayed high conversion yields at relatively high substrate concentrations, a promising feature for industrial application. Starch is the second-most-abundant carbohydrate on earth and a major dietary carbohydrate for humans; as a storage carbohydrate it is present in seeds, roots, and tubers of plants (1). It consists of ␣-glucan polymers with ␣1¡4 linkages and a low percentage of ␣1¡6 linkages, in the form of amylose and branched amylopectin (2). Starches are applied in various industrial products such as food, paper, and textiles, often after processing by physical, chemical, or enzymatic treatment (3-6).Dietary fibers and low-glycemic-index (low-GI) food are considered healthy food contributing to our long-term well-being (7,8). Of all the nutritional types of starch, slowly digestible starch with low GI has drawn the strongest interest. Annealing/heatmoisture treatment, recrystallization, and enzymatic treatment are recognized approaches to obtain slowly digestible starch (9-11). Slowly digestible starch materials prepared by physical processing suffer losses upon boiling; therefore, structural modifications through enzymatic treatment of starch are more desirable. In the human digestive system, the ␣1¡6 linkages in starch are hydrolyzed at a lower rate than ␣1¡4 linkages (12, 13). Branching enzymes, alone or in combination with ␤-amylase, are used to increase the percentage of ␣1¡4,6 branches in starches (12)(13)(14).The 4,6-␣-glucanotransferase (4,6-␣-GTase) enzymes, such as GTFB, GTFW, and GTFML4, of Lactobacillus reuteri strains constitute a subfamily of glycoside hydrolase family 70 (GH70); GH70 ...

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Section: Figmentioning

confidence: 99%