Purification and some properties of a novel maltohexaose-producing exo-amylase from Aerobacter aerogenes

Dietary Alaska pollock protein alters insulin sensitivity and gut microbiota composition in rats

Fish protein is not only nutritional but also promotes health by improving insulin sensitivity and hypercholesterolemia. Few studies have examined the relationship between gut microbiota and the enhanced insulin sensitivity due to the intake of Alaska pollock protein (APP). Hence, we assessed the glycolytic enzyme inhibitory activity of APP in in vitro study and the alteration of blood glucose level in insulin tolerance test (ITT) and glucose tolerance test (GTT) and gut microbiota following APP intake in the in vivo study. In initial experiments, the glycolytic enzyme (α-amylase, α-glucosidase, and sucrase) inhibitory activities of APP and its digest were not drastically altered compared with that of casein and its digests. In further experiments, rats fed an AIN-93G diet containing 20% (w/w) casein or APP for 8 weeks, and the composition of fecal microbiota analyzed by 16S rRNA amplicon sequence analysis. In addition, at 6 and 7 weeks of administration of experimental diet, insulin and glucose tolerance tests were evaluated, respectively. Compared with dietary casein, dietary APP has blood glucose-lowering activity as evident in the ITT and GTT. Moreover, APP group altered the structure of fecal microbiota, and area under the curves of the ITT and GTT and the relative abundance of Blautia, which is associated with glucose metabolism, tended to be positively correlated (P = 0.08 and 0.10, respectively). This study illustrates a novel finding that APP intake could alter the composition of gut microbiota and improve insulin sensitivity. PRACTICAL APPLICATION: Studies in animals and humans have shown that Alaska pollock protein (APP) intake improves insulin sensitivity, allowing the body to utilize blood glucose more effectively, thereby keeping blood sugar levels under control. Microorganisms residing in the human gut are associated with glucose metabolism. This study shows that the relative APP intake alters the composition of these gut microorganisms, more than casein intake and therefore might prevent hyperglycemia and type 2 diabetes.

Purification and characterization of a maltooligosaccharide-forming amylase that improves product selectivity in water-miscible organic solvents, from dimethylsulfoxide-tolerant Brachybacterium sp. strain LB25

A bacterium that secretes maltooligosaccharide-forming amylase in a medium containing 12.5% (vol/vol) dimethylsulfoxide (DMSO) was isolated and identified as Brachybacterium sp. strain LB25. The amylase of the strain was purified from the culture supernatant, and its molecular mass was 60 kDa. The enzyme was stable at pH 7.0-8.5 and active at pH 6.0-7.5. The optimum temperature at pH 7.0 was 35 degrees C in the presence of 5 mM CaCl(2). The enzyme hydrolyzed starch to produce maltotriose primarily. The enzyme was active in the presence of various organic solvents. Its yield and product selectivity of maltooligosaccharides in the presence of DMSO or ethanol were compared with those of the industrial maltotriose-forming amylase from Microbacterium imperiale. Both enzymes improved the production selectivity of maltotriose by the addition of DMSO or ethanol. However, the total maltooligosaccharide yield in the presence of the solvents was higher for LB25 amylase than for M. imperiale amylase.

Haloalkaliphilic maltotriose-forming alpha-amylase from the archaebacterium Natronococcus sp. strain Ah-36

A haloalkaliphilic archaebacterium, Natronococcus sp. strain Ah-36, produced extracellularly a maltotriose-forming amylase. The amylase was purified to homogeneity by ethanol precipitation, hydroxylapatite chromatography, hydrophobic chromatography, and gel filtration. The molecular weight of the enzyme was estimated to be 74,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The amylase exhibited maximal activity at pH 8.7 and 55 degrees C in the presence of 2.5 M NaCl. The activity was irreversibly lost at low ionic strength. KCl, RbCl, and CsCl could partially substitute for NaCl at higher concentrations. The amylase was stable in the range of pH 6.0 to 8.6 and up to 50 degrees C in the presence of 2.5 M NaCl. Stabilization of the enzyme by soluble starch was observed in all cases. The enzyme activity was inhibited by the addition of 1 mM ZnCl2 or 1 mM N-bromosuccinimide. The amylase hydrolyzed soluble starch, amylose, amylopectin, and, more slowly, glycogen to produce maltotriose with small amounts of maltose and glucose of an alpha-configuration. Malto-oligosaccharides ranging from maltotetraose to maltoheptaose were also hydrolyzed; however, maltotriose and maltose were not hydrolyzed even with a prolonged reaction time. Transferase activity was detected by using maltotetraose or maltopentaose as a substrate. The amylase hydrolyzed gamma-cyclodextrin. alpha-Cyclodextrin and beta-cyclodextrin, however, were not hydrolyzed, although these compounds acted as competitive inhibitors to the amylase activity. Amino acid analysis showed that the amylase was characteristically enriched in glutamic acid or glutamine and in glycine.

Cloning, nucleotide sequence, and enzymatic characterization of an alpha-amylase from the ruminal bacterium Butyrivibrio fibrisolvens H17c

A Butyrivibrio fibrisolvens amylase gene was cloned and expressed by using its own promoter on the recombinant plasmid pBAMY100 in Escherichia coli. The amylase gene consisted of an open reading frame of 2,931 bp encoding a protein of 976 amino acids with a calculated Mr of 106,964. In E. coli(pBAMY100), more than 86% of the active amylase was located in the periplasm, and TnphoA fusion experiments showed that the enzyme had a functional signal peptide. The B. fibrisolvens amylase is a calcium metalloenzyme, and three conserved putative calcium-binding residues were identified. The amylase showed high sequence homology with other alpha-amylases in the three highly conserved regions which constitute the active centers. These and other conserved regions were located in the N-terminal half, and no similarity with any other amylase was detected in the remainder of the protein. Deletion of approximately 40% of the C-terminal portion of the amylase did not result in loss of amylolytic activity. The B. fibrisolvens amylase was identified as an endo-alpha-amylase by hydrolysis of the Phadebas amylase substrate, hydrolysis of gamma-cyclodextrin to maltotriose, maltose, and glucose and the characteristic shape of the blue value and reducing sugar curves. Maltotriose was the major initial hydrolysis product from starch, although extended incubation resulted in its hydrolysis to maltose and glucose.

Microbial amylolytic enzymes

Starch-degrading, amylolytic enzymes are widely distributed among microbes. Several activities are required to hydrolyze starch to its glucose units. These enzymes include alpha-amylase, beta-amylase, glucoamylase, alpha-glucosidase, pullulan-degrading enzymes, exoacting enzymes yielding alpha-type endproducts, and cyclodextrin glycosyltransferase. Properties of these enzymes vary and are somewhat linked to the environmental circumstances of the producing organisms. Features of the enzymes, their action patterns, physicochemical properties, occurrence, genetics, and results obtained from cloning of the genes are described. Among all the amylolytic enzymes, the genetics of alpha-amylase in Bacillus subtilis are best known. Alpha-Amylase production in B. subtilis is regulated by several genetic elements, many of which have synergistic effects. Genes encoding enzymes from all the amylolytic enzyme groups dealt with here have been cloned, and the sequences have been found to contain some highly conserved regions thought to be essential for their action and/or structure. Glucoamylase appears usually in several forms, which seem to be the results of a variety of mechanisms, including heterogeneous glycosylation, limited proteolysis, multiple modes of mRNA splicing, and the presence of several structural genes.

Amylases: enzymatic mechanisms

Many types of amylases are found throughout the animal, vegetable and microbial kingdoms. They have evolved along different pathways to enable the organism to convert insoluble starch (or glycogen) into low molecular weight, water soluble dextrins and sugars. Alpha amylases are dextrinogenic and can attack the interior of starch molecules. The products retain the alpha anomeric configuration. Beta amylases act only at the non-reducing chain ends and liberate only beta maltose. Both alpha and beta amylases exhibit multiple (repetitive) attack, that is, after the initial catalytic cleavage, the enzyme may remain attached to the substrate and lead to several more cleavages before dissociation of the enzyme-substrate complex. Amylases have extended substrate binding sites, in the range 4-9 glucose units. This enables the enzyme to stress the substrate and lower the activation energy for hydrolysis. Similarly the enzyme exerts a torsion on the glucose unit at the catalytic site, inducing a transition state conformation (oxycarbonium ion). Alpha and beta amylases differ in the stereospecific hydration of the oxycarbonium ion, in the sequence of liberation of the right-hand vs the left-hand product, and the direction of motion of the retained substrate to give multiple attack.

Action of Pseudomonas isoamylase on various branched oligo and poly-saccharides

Pseudomonas isoamylase (EC 3.2.1.68) hydrolyzes (1 linked to 6)-alpha-D-glucosidic linkages of amylopectin, glycogen, and various branched dextrins and oligosaccharides. The detailed structural requirements for the substrate are examined qualitatively and quantitatively in this paper, in comparison with the pullulanase of Klebsiella aerogenes. As with pullulanase, Ps. isoamylase is unable to cleave D-glucosyl stubs from branched saccharides. Ps. isoamylase differs from pullulanase in the following characteristics: (1) The favored substrates for Ps. isoamylase are higher-molecular-weight polysaccharides. Most of the branched oligosaccharides examined were hydrolyzed at a lower rate, 10% or less of the rate of hydrolysis of amylopectin. (2) Maltosyl branches are hydrolyzed off by Ps. isoamylase very slowly in comparison with maltotriosyl branches. (3) Ps. isoamylase requires a minimum of three D-glucose residues in the B- or C-chain.

[Cyclodextrin glucanotransferase from Klebsiella pneumoniae. 1. Formation, purification and properties of the enzyme from Klebsiella pneumoniae M 5 al (author's transl)]

1. The strain M 5 al of Klebsiella pneumoniae grows excellently with starches. We were able to show that besides the pullulanase associated with the external membrane of the cells the bacterium produces an inducible, extracellular cyclodextrin glucanotransferase [1,4-alpha-D-glucan-4-alpha-(1,4-alpha-glucano)-transferase (cyclising) (EC 2.4.1.19)]. Potato starch and cyclohexaamylose or cycloheptaamylose were found to be the best "inducing" carbon sources for the synthesis of the enzyme. When the bacteria are grown batchwise, maltose is a poorly "inducing" carbon source; larger quantities of the enzyme are synthesized by continuous cultivation with maltose as growth limiting factor. 2. For the determination of the cyclodextrin glucanotransferase-activity an assay method wsa worked out. 3. The enzyme could be separated from the culture filtrate and purified to more than 90% in few steps. At a total yield of 61.2% related to the activity of the culture filtrate employed we received an enzyme solution with the specific activity of 26.6 units/mg protein. Some properties of the enzyme are described. 4. The products formed from amylopectin by the enzyme were analyzed. Somewhat more than half the amylopectin was found as cyclodextrins. 29.3% of the cyclodextrin fraction were cycloheptaamylose, 47.2% cyclohexaamylose and 10.7% exo-branched cyclohexaamylose. 12.8% of cyclohexaamylose were obtained from a cyclodextrin glucanotransferase-limit dextrin after debranching by pullulanase and exposing the product to the action of the glucanotransferase again. 5. The importance of the cyclodextrin glucanotransferase for the utilization of starches by this strain of Klebsiella pneumoniae is discussed. After a first characterization the enzyme is compared to the amylase of Bacillus macerans.