The starch-binding domain from glucoamylase disrupts the structure of starch.
(9/1890)
The full-length glucoamylase from Aspergillus niger, G1, consists of an N-terminal catalytic domain followed by a semi-rigid linker (which together constitute the G2 form) and a C-terminal starch-binding domain (SBD). G1 and G2 both liberate glucose from insoluble corn starch, although G2 has a rate 80 times slower than G1. Following pre-incubation of the starch with SBD, the activity of G1 is uniformly reduced with increasing concentrations of SBD because of competition for binding sites. However, increasing concentrations of SBD produce an initial increase in the catalytic rate of G2, followed by a decrease at higher SBD concentrations. The results show that SBD has two functions: it binds to the starch, but it also disrupts the surface, thereby enhancing the amylolytic rate. (+info)
Dietary chromic oxide does not affect the utilization of organic compounds but can alter the utilization of mineral salts in gilthead sea bream Sparus aurata.
(10/1890)
This study was conducted to determine whether the level of chromic oxide supplemented to diets containing gelatinized starch as the carbohydrate source affects digestibility, body composition, growth performances, and liver enzyme activities in gilthead sea bream, Sparus aurata. Gilthead sea bream fingerlings were fed diets containing gelatinized corn starch as the carbohydrate source and several levels of chromic oxide (0, 5, 10 and 20 g/kg) for 6 wk. No effect of dietary chromium level was detected on carbon, nitrogen, or dry matter digestibility. Calcium and phosphorus digestibility were higher in fish fed the diet supplemented with 5 g/kg chromic oxide than in fish fed the other supplemented diets. Dietary chromium did not affect dry matter, carbon, nitrogen, protein, or lipid concentrations in fish. However, fish fed 5 g/kg chromic oxide generally had higher levels of calcium, phosphorus, and ash than fish fed the other Cr-containing diets. Chromium concentration was significantly higher in fish fed the diets with 0.5 and 1% chromic oxide than in fish fed the control diet. Chromium supplementation of the diets did not affect the specific growth rate, the food efficiency ratio, the protein efficiency ratio, or, protein or nitrogen retention of the fish. Blood glucose and the activity of several liver enzymes involved in carbohydrate metabolism were unaffected by dietary chromic oxide. Alanine aminotransferase was lower in the fish fed the diet with 10 g/kg of chromic oxide than in unsupplemented controls. Our results indicate that chromic oxide can be used as a neutral marker in fish nutrition studies involving organic compounds, but not mineral salts. (+info)
Potential of short chain fatty acids to modulate the induction of DNA damage and changes in the intracellular calcium concentration by oxidative stress in isolated rat distal colon cells.
(11/1890)
Short chain fatty acids (SCFA) are considered to be beneficial fermentation products in the gut by exerting trophic effects in non-transformed colon cells and by slowing proliferation and enhancing differentiation in colonic tumour cells. We have studied the further effects of SCFA on cellular events of early carcinogenesis, genotoxicity and cytotoxicity in rat distal colon cells. Cytotoxicity was assessed by measuring trypan blue exclusion and by determining the H2O2-induced changes in intracellular calcium concentration ([Ca2+]i) using a fluorospectrophotometer and the calcium-sensitive fluorescent dye Fura-2. The microgel electrophoresis technique (COMET assay) was used to assess oxidative DNA damage. Individual SCFA and physiological SCFA mixtures were investigated for their potential to prevent DNA and cell damage induced by H2O2. For this, freshly isolated colon cells were treated with H2O2 (100-500 microM) and 6.25 mM SCFA. We have found 100-500 microM H2O2 to cause a fast initial increase in [Ca2+]i, whereafter the levels gradually further increased. Addition of SCFA did not affect [Ca2+]i nor did it reduce the H2O2-induced increase in [Ca2+]i. Butyrate and acetate were able to reduce the induction of DNA damage by 100, 200 and 500 microM H2O2, respectively. In contrast, i-butyrate and propionate were ineffective. The degree of reduction of DNA damage for the two protective SCFA was similar. Physiological mixtures containing acetate, propionate and butyrate in ratios of 41:21:38 or 75:15:10 that are expected to arise in the colon after fermentation of resistant starches and pectin, respectively, did not show significant antigenotoxic effects. The major difference between butyrate and acetate, on one hand, and i-butyrate and propionate, on the other hand, is that the former compounds are utilized best as energy sources by the colon cells. Therefore, our results on antigenotoxicity coupled with the findings on [Ca2+]i homeostasis indicate that molecular effects on the energy system render these non-transformed, freshly isolated colon cells to be less susceptible to H2O2. (+info)
Stable, inducible thermoacidophilic alpha-amylase from Bacillus acidocaldarius.
(12/1890)
Bacillus acidocaldarius Agnano 101 produces an inducible thermoacidophilic alpha-amylase. The enzyme production occurs during the stationary phase of growth in the presence of compounds with alpha-1,4-glucosidic linkages. The enzymatic activity is both present in the culture medium and associated with the cells; the enzymes purified from both sources show identical molecular and catalytic properties. The purified amylase has a single polypeptide chain of molecular weight 68,000 and behaves like an alpha-amylase with affinity constants for starch and related substances of 0.8 to 0.9 mg/ml. The pH and temperature optima for activity are 3.5 and 75degreesC, respectively. The amylase is stable at acidic pH (below 4.5). Its thermal stability is strictly dependent upon protein concentration; the half-life at 60degreesC of the amylase in a 70-mug/ml solution is about 5 days. (+info)
Characterization of bacteroides melaninogenicus.
(13/1890)
Fifty-eight human isolates of Bacteroides melaninogenicus, 42 from a variety of clinical infections and the rest from normal flora, were studied for pigment production and ultraviolet light fluorescence and by forty biochemical and other tests, including end-product analysis by gas-liquid chromatography. In a number of instances, tests were repeated several times and the results were reproducible. Agar plate dilution susceptibility tests were also performed to 12 antimicrobial agents. These 58 strains could be reliably placed into three groups, corresponding to the three subspecies described, based on seven characteristics. These included acid production in peptone-yeast-glucose medium, production of n-butyric acid from peptone-yeast-glucose medium, esculin hydrolysis, starch hydrolysis, indole production, effect on milk, and lipase production. Production of hydrogen gas in peptone-yeast-fructose medium may be another distinguishing characteristic. In general there was not much difference in the susceptibility of the three groups to the various antimicrobial agents tested. Two strains had a minimal inhibitory concentration of penicillin G of 16 and 32 U/ml, respectively. Three strains did not produce a black pigment in spite of prolonged incubation on blood-containing media. (+info)
Plastid sedimentation kinetics in roots of wild-type and starch-deficient mutants of Arabidopsis.
(14/1890)
Sedimentation and movement of plastids in columella cells of the root cap were measured in seedlings of wild-type, a reduced starch mutant, and a starchless mutant of Arabidopsis. To assay for sedimentation, we used both linear measurements and the change of angle from the cell center as indices in vertical and reoriented plants with the aid of computer-assisted image analysis. Seedlings were fixed at short periods after reorientation, and plastid sedimentation correlated with starch content in the three strains of Arabidopsis. Amyloplasts of wild-type seedlings showed the greatest sedimentation, whereas plastids of the starchless mutant showed no significant sedimentation in the vertically grown and reoriented seedlings. Because previous research has shown that a full complement of starch is needed for full gravitropic sensitivity, this study correlates increased sensitivity with plastid sedimentation. However, although plastid sedimentation contributed to gravisensitivity, it was not required, because the gravitropic starchless mutant had plastids that did not sediment. This is the first study, to our knowledge, to measure plastid sedimentation in Arabidopsis roots after reorientation of seedlings. Taken together, the results of this study are consistent with the classic plastid-based and protoplast-based models of graviperception and suggest that multiple systems of perception exist in plant cells. (+info)
Splanchnic and leg substrate exchange after ingestion of a natural mixed meal in humans.
(15/1890)
The disposal of a mixed meal was examined in 11 male subjects by multiple (splanchnic and femoral) catheterization combined with double-isotope technique (intravenous [2-3H]glucose plus oral U-[14C]starch). Glucose kinetics and organ substrate balance were measured basally and for 5 h after eating pizza (600 kcal) containing carbohydrates 75 g as starch, proteins 37 g, and lipids 17 g. The portal appearance of ingested carbohydrate was maximal (1.0 mmol/min) between 30 and 60 min after the meal and gradually declined thereafter, but was still incomplete at 300 min (0.46+/-0.08 mmol/min). The total amount of glucose absorbed by the gut over the 5 h of the study was 247+/-26 mmol (45+/-6 g), corresponding to 60+/-6% of the ingested starch. Net splanchnic glucose balance (-6.7+/-0.5 micromol x kg(-1) x min(-1), basal) rose by 250-300% between 30 and 60 min and then returned to baseline. Hepatic glucose production (HGP) was suppressed slightly and only tardily in response to meal ingestion (approximately 30% between 120 and 300 min). Splanchnic glucose uptake (3.7+/-0.6 micromol x kg(-1) x min(-1), basal) peaked to 9.8+/-2.0 micromol x kg(-1) x min(-1) (P<0.001) at 120 min and then returned slowly to baseline. Leg glucose uptake (34+/-5 micromol x leg(-1) x min(-1), basal) rose to 151+/-29 micromol x leg(-1) x min(-1) at 30 min (P<0.001) and remained above baseline until the end of the study, despite no increase in leg blood flow. The total amount of glucose taken up by the splanchnic area and total muscle mass was 161+/-16 mmol (29+/-3 g) and 128 mmol (23 g), respectively, which represent 39 and 30% of the ingested starch. Arterial blood lactate increased by 30% after meal ingestion. Net splanchnic lactate balance switched from a basal net uptake (3.2+/-0.6 micromol kg(-1) x min(-1) to a net output between 60 and 120 min and tended to zero thereafter. Leg lactate release (25+/-11 micromol x leg(-1) x min(-1), basal) drastically decreased postprandially. Arterial concentration of both branched-chain amino acids (BCAA) and non-branched-chain amino acids (N-BCAA) increased significantly after meal ingestion (P<0.001). The splanchnic area switched from a basal net amino acid uptake (31+/-16 and 92+/-48 micromol/min for BCAA and N-BCAA, respectively) to a net amino acid release postprandially. The net splanchnic amino acid release over 5 h was 11.3+/-4.2 mmol for BCAA and 37.8+/-9.7 mmol for N-BCAA. Basally, the net leg balance of BCAA was neutral (-3+/-5 micromol x leg(-1) x min(-1)), whereas that of N-BCAA indicated a net release (54+/-14 micromol x leg(-1) x min(-1)). After meal ingestion, there was a net leg uptake of BCAA (20+/-6 micromol x leg(-1) x min(-1)), whereas leg release of N-BCAA decreased by 50%. It is concluded that in human subjects, 1) the absorption of a natural mixed meal is still incomplete at 5 h after ingestion; 2) HGP is only marginally and tardily inhibited; 3) splanchnic and peripheral tissues contribute to the disposal of meal carbohydrate to approximately the same extent; 4) the splanchnic area transfers >30% of the ingested proteins to the systemic circulation; and 5) after meal ingestion, skeletal muscle takes up BCAA to replenish muscle protein stores. (+info)
Intestinal tumorigenesis in the Apc1638N mouse treated with aspirin and resistant starch for up to 5 months.
(16/1890)
The Apc1638N mouse model, which carries a targeted mutant allele within the adenomatous polyposis (Apc) gene and develops intestinal tumours spontaneously, predominantly in the small bowel, was used to investigate the effects of two potential chemopreventive agents, aspirin and alpha-amylase resistant starch (RS). Heterozygous Apc+/Apc1638N mice were fed semi-purified diets rich in animal fat, animal proteins and sucrose and low in dietary fibre (Western style diets) from approximately 6 weeks up to 6 months of age. Two of the diets contained aspirin (300 mg/kg diet) and two RS (1:1 mixture of raw potato starch: Hylon VII at 200 g/kg diet) in a 2 x 2 factorial design. A fifth treatment group were fed a conventional rodent chow diet. The mice fed the Western style diets became almost three times as fat as the chow-fed mice but this did not affect tumour yield. Treatment with RS resulted in significantly more intestinal tumours whereas aspirin alone had no effect. However, there was a significant aspirin x RS interaction, which suggests that aspirin could prevent the small intestine tumour-enhancing effects of RS in this Apc-driven tumorigenesis model. The possibility that large amounts of purified forms of resistant starch may have adverse effects within the small bowel is a novel observation that requires further investigation since greater intakes of starchy foods (and of RS) are being encouraged as a public health measure in compensation for reduced dietary fat intake. However, it remains possible that any increased risk is restricted to carriers of germline mutations in APC. (+info)