Hydrolysis of low-molecular-weight oligosaccharides and oligosaccharide alditols by pig intestinal sucrase/isomaltase and glucosidase/maltase

Structural Analysis of the Catalytic Mechanism and Substrate Specificity of Anabaena Alkaline Invertase InvA Reveals a Novel Glucosidase

Invertases catalyze the hydrolysis of sucrose to glucose and fructose, thereby playing a key role in primary metabolism and plant development. According to the optimum pH, invertases are classified into acid invertases (Ac-Invs) and alkaline/neutral invertases (A/N-Invs), which share no sequence homology. Compared with Ac-Invs that have been extensively studied, the structure and catalytic mechanism of A/N-Invs remain unknown. Here we report the crystal structures of Anabaena alkaline invertase InvA, which was proposed to be the ancestor of modern plant A/N-Invs. These structures are the first in the GH100 family. InvA exists as a hexamer in both crystal and solution. Each subunit consists of an (α/α)₆ barrel core structure in addition to an insertion of three helices. A couple of structures in complex with the substrate or products enabled us to assign the subsites -1 and +1 specifically binding glucose and fructose, respectively. Structural comparison combined with enzymatic assays indicated that Asp-188 and Glu-414 are putative catalytic residues. Further analysis of the substrate binding pocket demonstrated that InvA possesses a stringent substrate specificity toward the α1,2-glycosidic bond of sucrose. Together, we suggest that InvA and homologs represent a novel family of glucosidases.

Wheat-barley-rye- or corn-fed growing pigs respond differently to dietary supplementation with a carbohydrase complex

Thirty-six pigs (22 kg of BW) were used to evaluate a carbohydrase preparation, with xylanase and β-glucanase as main activities, added to either wheat-barley-rye- (WBR) or corn-based diets on performance, intestinal environment, and nutrient digestibility. Pigs were offered 1 of 4 different dietary treatments for 27 d according to a factorial arrangement of treatments (a 2 × 2) with 2 cereal types (WBR or corn) and 2 levels of supplemental carbohydrase (0 or 0.01%). Pig growth and feed intake were individually measured every week until the end of the experiment when pigs were slaughtered to obtain samples of digesta and tissues. Cereal type affected performance only during wk 1, in which WBR improved ADG (590 vs. 440 g/d; P = 0.008) and G:F (0.61 vs. 0.43; P = 0.045) compared with corn. The WBR also increased the viscosity of the digestive contents in stomach (1.95 vs. 1.23 mPa·s; P = 0.001) and ileum (6.53 vs. 2.80 mPa·s; P = 0.001) and resulted in greater cecal starch digestibility (95.7 vs. 93.9%; P = 0.012). However, trends for a reduction in digestibility were observed for glucose in the nonstarch polysaccharide (NSP) fraction in the ileum (64.4 vs. 75.8%; P = 0.074) and galactose in the NSP fraction in the cecum (1.4 vs. 1.8%; P = 0.055). The use of the enzyme preparation increased ADFI during wk 2 (1,328 vs. 1,215 g/d; P = 0.028), and increased villus height (423 vs. 390 µm; P = 0.045) and tended to reduce relative pancreas weight (0.16 vs. 0.17% BW; P = 0.079) at d 27. The enzyme also improved cecal starch digestibility (95.5 vs. 94.1%; P = 0.043) and tended to improve ileal energy digestibility (61.3 vs. 53.7%; P = 0.090) and cecal glucose digestibility in the NSP fraction (76.0 vs. 54.5%; P = 0.055). However, it reduced the cecal digestibility of mannose in the NSP fraction (27.0 vs. 50.5%; P = 0.016). Interactions (P < 0.05) between cereal type and enzyme supplementation were observed for ADG and G:F during wk 2, BW and ADG during wk 3, and BW and ADFI over the whole trial; and also for villus-height-to-crypt-depth ratio and for cecal DM digestibility. In all instances, whereas the added enzyme had no effect in the case of the corn diet, improvements were observed with WBR. In conclusion, the multi-enzyme tested had different effects depending on the type of cereal present in the diet.

The synthesis of 2-, 3-, 4- and 6-O-α-d-glucopyranosyl-d-galactopyranose, and their evaluation as nutritional supplements for pre-term infants

Four methods have been screened for the synthesis of some alpha-D-glucopyranosides, with the recently reported (Mukaiyama) combination of 2,3,4,6-tetra-O-benzyl-alpha-D-glucopyranosyl iodide and triphenylphosphine oxide being the most successful, especially in the diastereoselectivity exhibited. The alpha-D-glucopyranosides so obtained have been deprotected to yield 2-, 3-, 4- and 6-O-alpha-D-glucopyranosyl-D-galactopyranose. Only the last disaccharide showed any hydrolysis by alpha-glycosidases but this success was not emulated by mucosal extracts from the small intestine of the pig.

Effects of isomalto-oligosaccharides on broiler performance and intestinal microflora

Dose effects of dietary isomalto-oligosacchrides (IMO) on broiler growth performance and characteristics of the intestinal microflora were compared. Three hundred sixty male broilers were randomly allotted to five treatments, with eight replicate pens per treatment and nine chicks per pen. Chicks were fed either a basal diet (control) or the basal diet plus 0.3, 0.6, 0.9, or 1.2% IMO. All chicks had access to feed and water ad libitum during the 7-wk experiment. At the end of the experiment, eight chicks per treatment were randomly chosen to measure the thymus index. Additionally, six birds per treatment were randomly selected to determine viable bacterial counts of Lactobacillus, Escherichia coli, and total aerobes in the digestive tract. The digesta of all the killed birds were also used to measure short-chain fatty acid (SCFA) levels. The results indicate that IMO enhanced growth performance during the initial 3 wk, but no further effects were detected during the latter 4 wk of the experiment. Isobutyrate level in crop content and acetate level in duodenum digesta were decreased by supplementation with IMO (P < 0.05). Isovalerate level in duodenum digesta was decreased in the 0.3 and 0.6% IMO groups (P < 0.001), whereas the jejunum butyrate and isobutyrate levels of the 0.3% IMO group were higher than in other groups (P < 0.05). The facultative microflora of the crop and cecum were not affected by IMO supplementation. However, the thymus index was increased significantly in chicks consuming diets containing 0.3% IMO.

Methods of in vitro toxicology

In vitro methods are common and widely used for screening and ranking chemicals, and have also been taken into account sporadically for risk assessment purposes in the case of food additives. However, the range of food-associated compounds amenable to in vitro toxicology is considered much broader, comprising not only natural ingredients, including those from food preparation, but also compounds formed endogenously after exposure, permissible/authorised chemicals including additives, residues, supplements, chemicals from processing and packaging and contaminants. A major promise of in vitro systems is to obtain mechanism-derived information that is considered pivotal for adequate risk assessment. This paper critically reviews the entire process of risk assessment by in vitro toxicology, encompassing ongoing and future developments, with major emphasis on cytotoxicity, cellular responses, toxicokinetics, modelling, metabolism, cancer-related endpoints, developmental toxicity, prediction of allergenicity, and finally, development and application of biomarkers. It describes in depth the use of in vitro methods in strategies for characterising and predicting hazards to the human. Major weaknesses and strengths of these assay systems are addressed, together with some key issues concerning major research priorities to improve hazard identification and characterisation of food-associated chemicals.

Chapter 16 Production and gene expression of brush border disaccharidases and peptidases during development in pigs and calves

This chapter reviews the expression of intestinal brush-border disaccharidases (maltase-glucoamylase, sucrase-isomaltase, lactase, and trehalase) and peptidases (aminopeptidases A and N and dipeptidyl peptidase IV) during development in growing animals. It describes the roles of intestinal enzymes, focussing on complementarity with salivary, gastric, and pancreatic digestive enzymes and their hydrolytic function in the process of absorption. Gene expression of the enzymes and nutritional regulation of their expression appear during postnatal development up to maturity. After translation of the specific mRNA, a single precursor of maltaseglucoamylase (pro-MG), rich in mannose, is produced in the rough endoplasmic reticulum (RER). In contrast to the relatively small number of carbohydrases, the number of peptidases found in enterocytes in the small intestine is large, because of the large number of different peptide bonds in oligopeptides produced by the action of pancreatic proteases. The digestive function (disaccharidase and peptidase activities) of the enterocytes and their microvilli begins when structural differentiation is complete, that is, during the period of migration over the cryptvillus junction. Modern techniques and investigations are expected to yield relevant data for elaborating feeding strategies that take into account the complex interactions between the diet, the microflora, the luminal milieu and the physiology of the small intestine, including the optimal functioning of the immunological and endocrine systems.