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At least 847 records · Page 47Linked to original sources
PubMed2000

Mutation of Arabidopsis plastid phosphoglucose isomerase affects leaf starch synthesis and floral initiation.

We isolated pgi1-1, an Arabidopsis mutant with a decreased plastid phospho-glucose (Glc) isomerase activity. While pgi1-1 mutant has a deficiency in leaf starch synthesis, it accumulates starch in root cap cells. It has been shown that a plastid transporter for hexose phosphate transports cytosolic Glc-6-P into plastids and expresses restricted mainly to the heterotrophic tissues. The decreased starch content in leaves of the pgi1-1 mutant indicates that cytosolic Glc-6-P cannot be efficiently transported into chloroplasts to complement the mutant's deficiency in chloroplastic phospho-Glc isomerase activity for starch synthesis. We cloned the Arabidopsis PGI1 gene and showed that it encodes the plastid phospho-Glc isomerase. The pgi1-1 allele was found to have a single nucleotide substitution, causing a Ser to Phe transition. While the flowering times of the Arabidopsis starch-deficient mutants pgi1, pgm1, and adg1 were similar to that of the wild type under long-day conditions, it was significantly delayed under short-day conditions. The pleiotropic phenotype of late flowering conferred by these starch metabolic mutations suggests that carbohydrate metabolism plays an important role in floral initiation.

Amino Acid Sequence↗
PubMed1969

Enzymic degradiation of starch granules in the cotyledons of germinating peas.

Starch, total alpha- and beta-amylase, and phosphorylase levels and the zymogram patterns of these 3 starch-degrading enzymes were determined in the cotyledons of smooth pea (Pisum sativum L.) during the first 15 days of germination. Starch is degraded slowly in the first 6 days; during this time, alpha-amylase is very low, beta-amylase is present at a constant level while phosphorylase gradually increases and reaches a peak on the fifth day. Beginning on the sixth day there is a more rapid degradation of starch which coincides with alpha-amylase production. One phosphorylase band and 2 beta-amylase bands are present in the zymogram of the imbibed cotyledon. An additional phosphorylase band and 1 alpha-amylase band appear during germination. Seeds imbibed in benzyladenine, chloramphenicol, and in cycloheximide show retarded growth and slower starch degradation and enzyme production than the controls. We conclude that alpha-amylase is the major enzyme involved in the initial degradation of starch into more soluble forms while phosphorylase and beta-amylase assist in the further conversion to free sugars.

Amylases↗
PubMed2003

Mutational analysis of the pullulanase-type debranching enzyme of maize indicates multiple functions in starch metabolism.

Plants contain two types of alpha(1-->6) glucan hydrolase (starch-debranching enzyme [DBE]). Mutations that affect the pullulanase-type DBE have not been described, although defects in isoamylase-type DBE, known in many plant species, indicate a function in starch biosynthesis. We describe a null mutation of a pullulanase-type DBE gene, a Mutator insertion in maize Zpu1. Plants homozygous for the zpu1-204 mutation are impaired in transient and storage starch degradation. Thus, hydrolytic activity of pullulanase-type DBE contributes to starch catabolism. Developing zpu1-204 endosperm accumulates branched maltooligosaccharides not found in the wild type and is deficient in linear maltooligosaccharides, indicating that the pullulanase-type DBE functions in glucan hydrolysis during kernel starch formation. Furthermore, in a background deficient in isoamylase-type DBE, zpu1-204 conditions a significant accumulation of phytoglycogen in the kernel that is not seen in the wild type. Therefore, pullulanase-type DBE partially compensates for the defect in isoamylase-type DBE, suggesting a function during starch synthesis as well as degradation.

Alleles↗
PubMed1996

Identification of the major starch synthase in the soluble fraction of potato tubers.

The major isoform of starch synthase from the soluble fraction of developing potato tubers has been purified and used to prepare an antibody and isolate a cDNA. The protein is 140 kD, and it is distinctly different in predicted primary amino acid sequence from other isoforms of the enzyme thus far described. Immunoinhibition and immunoblotting experiments and analysis of tubers in which activity of the isoform was reduced through expression of antisense mRNA revealed that the isoform accounts for approximately 80% of the activity in the soluble fraction of the tuber and that it is also bound to starch granules. Severe reductions in activity had no discernible effect on starch content or amylose-to-amylopectin ratio of starch in tubers. However, they caused a profound change in the morphology of starch granules, indicative of important underlying changes in the structure of starch polymers within the granule.

Amino Acid Sequence↗
PubMed2002

Influence of modified starches on the stability of beef jerky analogs during storage.

Textural stabilization of extruded beef jerky analogs (BJA) by using modified starches was studied. From a series of modified starches studied, Frigex W and Instant Pure Flo were identified to show very reduced retrogradation, both in gels and after extrusion. These starches were used as textural stabilizers for BJA, an extruded product obtained from potato granules and ground beef. The partial substitution of potato granules with modified starches, at a level of 5% of the formulation, led to increased moisture sorption capacity of the analogs. After a storage period of 1 mo, the samples that contained modified starch had a degree of swelling with 30% higher and much lower elastic modulus as compared to those that contained only potato starch.

Food Preservation↗
PubMed1986

Starch utilization by the human large intestinal microflora.

High levels (2-565 units/g) of amylase activity were observed in human faeces. Over 92% of amylase activity in faeces obtained from healthy persons was extracellular, whereas only about 9% of activity was associated with particulate material and washed cells. Bacterial cell-bound amylases were considerably more efficient in breaking down starch, however, than were the soluble enzymes which occurred in cell-free faecal supernatant fluids. Cell population densities of anaerobic starch-hydrolysing bacteria in the stools of ten persons ranged from 1.1 X 10(10) to 3.3 X 10(12)/g of faeces. Identification of 120 starch-hydrolysing colonies isolated from the stools of six subjects showed that the predominant amylolytic bacteria belonged to the genera Bifidobacterium, Bacteroides, Fusobacterium and Butyrivibrio. Mixed populations of gut bacteria rapidly fermented starch with the production of volatile fatty acids and organic acids. Lactate was observed to be a major, though transient intermediate during starch fermentation by these cultures. Approximately 60% of starch utilized was converted to volatile fatty acids, which in the human colon would be potentially available for absorption.

Amylases↗
PubMed2005

Solid-state fermentation of cornmeal with the basidiomycete Ganoderma lucidum for degrading starch and upgrading nutritional value.

AIMS: The objective of this research was to study the ability of the basidiomycete Ganoderma lucidum to degrade starch and upgrade nutritional value of cornmeal during solid-state fermentation (SSF). METHODS AND RESULTS: On the basal medium that consisted of cornmeal and salt solution, alpha-amylase activity of G. lucidum reached its maximum value of 267 U g(-1) of culture on day 20 after inoculation. Prolongation of fermentation time from 10 to 25 days increased significantly the degradation rate of starch and ergosterol yield (a kind of physiologically active substances of G. lucidum, also as an indicator of mycelial biomass) (P < 0.01). Supplementation of glucose, sucrose or maltose to the basal medium also caused a significant increase in either the degradation rate of starch or the ergosterol yield as compared with control (P < 0.01). Among five kinds of nitrogen sources supplemented, yeast extract, casamino acid and peptone were more effective than (NH4)2SO4 and NH4NO3, and yeast extract gave the highest degradation rate of starch and ergosterol yield, followed by peptone. Through orthogonal experiments, the theoretical optimum culture medium for SSF of this fungus was the following: 100 g cornmeal, ground to 30-mesh powder, moistened with 67 ml of nutrient salt solution supplemented with 3 g yeast extract and 7.5 g glucose per litre. CONCLUSIONS: Under the optimum culture condition, the degradation rate of starch reached its maximum values of 70.4%; the starch content of the fermented product decreased from 64.5 to 25.3%, while the reducing sugar content increased from 4.2 to 20.6%. SSF also produced a significant increase (P < 0.01) from 11.0 to 16.5% in protein content. SIGNIFICANCE AND IMPACT OF THE STUDY: After SSF by G. lucidum, the digesting and absorbing ratio of cornmeal was strikingly increased and some active substances originated from G. lucidum remained in the fermented product. This implied that cornmeal could be processed into many kinds of special functional foods by SSF of G. lucidum.

Biomass↗
PubMed2004

A cytosolic glucosyltransferase is required for conversion of starch to sucrose in Arabidopsis leaves at night.

Maltose is exported from the Arabidopsis chloroplast as the main product of starch degradation at night. To investigate its fate in the cytosol, we characterised plants with mutations in a gene encoding a putative glucanotransferase (disproportionating enzyme; DPE2), a protein similar to the maltase Q (MalQ) gene product involved in maltose metabolism in bacteria. Use of a DPE2 antiserum revealed that the DPE2 protein is cytosolic. Four independent mutant lines lacked this protein and displayed a decreased capacity for both starch synthesis and starch degradation in leaves. They contained exceptionally high levels of maltose, and elevated levels of glucose, fructose and other malto-oligosaccharides. Sucrose levels were lower than those in wild-type plants, especially at the start of the dark period. A glucosyltransferase activity, capable of transferring one of the glucosyl units of maltose to glycogen or amylopectin and releasing the other, was identified in leaves of wild-type plants. Its activity was sufficient to account for the rate of starch degradation. This activity was absent from dpe2 mutant plants. Based on these results, we suggest that DPE2 is an essential component of the pathway from starch to sucrose and cellular metabolism in leaves at night. Its role is probably to metabolise maltose exported from the chloroplast. We propose a pathway for the conversion of starch to sucrose in an Arabidopsis leaf.

Arabidopsis↗
PubMed2004

Adjustment of diurnal starch turnover to short days: depletion of sugar during the night leads to a temporary inhibition of carbohydrate utilization, accumulation of sugars and post-translational activation of ADP-glucose pyrophosphorylase in the following light period.

A larger proportion of the fixed carbon is retained as starch in the leaf in short days, providing a larger store to support metabolism and carbon export during the long night. The mechanisms that facilitate this adjustment of the sink-source balance are unknown. Starchless pgm mutants were analysed to discover responses that are triggered when diurnal starch turnover is disturbed. Sugars accumulated to high levels during the day, and fell to very low levels by the middle of the night. Sugars rose rapidly in the roots and rosette after illumination, and decreased later in the light period. Global transcript profiling revealed only small differences between pgm and Col0 at the end of the day but large differences at the end of the night, when pgm resembled Col0 after a 4-6 h prolongation of the night and many genes required for biosynthesis and growth were repressed [Plant J. 37 (2004) 914]. It is concluded that transient sugar depletion at the end of the night inhibits carbon utilization at the start of the ensuing light period. A second set of experiments investigated the stimulation of starch synthesis in response to short days in wild-type Col0. In short days, sugars were very low in the roots and rosette at the end of the dark period, and after illumination accumulated rapidly in both organs to levels that were higher than in long days. The response resembles pgm, except that carbohydrate accumulated in the leaf as starch instead of sugars. A similar response was found after transfer from long to short days. Inclusion of sugar in the rooting medium attenuated the stimulation of starch synthesis. Post-translational activation of ADP-glucose pyrophosphorylase (AGPase) was increased in pgm, and in Col0 in short days. It is concluded that starch synthesis is stimulated in short day conditions because sugar depletion at the end of the night triggers a temporary inhibition of growth and carbohydrate utilization in the first part of the light period, leading to transient accumulation of sugar and activation of AGPase.

Arabidopsis↗
PubMed2005

Roles of isoamylase and ADP-glucose pyrophosphorylase in starch granule synthesis in rice endosperm.

Amyloplast-targeted green fluorescent protein (GFP) was used to monitor amyloplast division and starch granule synthesis in the developing endosperm of transgenic rice. Two classical starch mutants, sugary and shrunken, contain reduced activities of isoamylase1 (ISA1) and cytosolic ADP-glucose pyrophosphorylase, respectively. Dividing amyloplasts in the wild-type and shrunken endosperms contained starch granules, whereas those in sugary endosperm did not contain detectable granules, suggesting that ISA1 plays a role in granule synthesis at the initiation step. The transition from phytoglycogen to sugary-amylopectin was gradual in the boundary region between the inner and outer endosperms of sugary. These results suggest that the synthesis of sugary-amylopectin and phytoglycogen involved a stochastic process and that ISA1 activity plays a critical role in the stochastic process in starch synthesis in rice endosperm. The reduction of cytosolic ADP-glucose pyrophosphorylase activity in shrunken endosperm did not inhibit granule initiation but severely restrained the subsequent enlargement of granules. The shrunken endosperm often developed pleomorphic amyloplasts containing a large number of underdeveloped granules or a large cluster of small grains of amyloplasts, each containing a simple-type starch granule. Although constriction-type divisions of amyloplasts were much more frequent, budding-type divisions were also found in the shrunken endosperm. We show that monitoring GFP in developing amyloplasts was an effective means of evaluating the roles of enzymes involved in starch granule synthesis in the rice endosperm.

Glucans↗
PubMed2006

A chloroplast-localized dual-specificity protein phosphatase in Arabidopsis contains a phylogenetically dispersed and ancient carbohydrate-binding domain, which binds the polysaccharide starch.

Dual-specificity protein phosphatases (DSPs) are important regulators of a wide variety of protein kinase signaling cascades in animals, fungi and plants. We previously identified a cluster of putative DSPs in Arabidopsis (including At3g52180 and At3g01510) in which the phosphatase domain is related to that of laforin, the human protein mutated in Lafora epilepsy. In animal and fungal systems, the laforin DSP and the beta-regulatory subunits of AMP-regulated protein kinase (AMPK) and Snf-1 have all been demonstrated to bind to glycogen by a glycogen-binding domain (GBD). We present a bioinformatic analysis which shows that these DSPs from Arabidopsis, together with other related plant DSPs, share with the above animal and fungal proteins a widespread and ancient carbohydrate-binding domain. We demonstrate that DSP At3g52180 binds to purified starch through its predicted carbohydrate-binding region, and that mutation of key conserved residues reduces this binding. Consistent with its ability to bind exogenous starch, DSP At3g52180 was found associated with starch purified from Arabidopsis plants and suspension cells. Immunolocalization experiments revealed a co-localization with chlorophyll, placing DSP At3g52180 in the chloroplast. Gene-expression data from different stages of the light-dark cycle and across a wide variety of tissues show a strong correlation between the pattern displayed by transcripts of the At3g52180 locus and that of genes encoding key starch degradative enzymes. Taken together, these data suggest the hypothesis that plant DSPs could be part of a protein assemblage at the starch granule, where they would be ideally situated to regulate starch metabolism through reversible phosphorylation events.

Amino Acid Sequence↗
PubMed1995

Investigations on preileal digestion of starch from grain, potato and manioc in horses.

In this study preileal starch digestibility of starchy feeds (oats, corn, barley, potatoes, manioc) was determined in seven jejunofistulated horses. The grains were fed whole (oats, corn), rolled (oats, barley), crushed, ground and expanded (corn); the potatoes were fresh, the manioc rolled. Ground corn was also fed in combination with amylase. The feeds were fed partly isolated or in combination with alfalfa meal or hay (Table 1). At least four horses with a cannula in the terminal jejunum were used for each diet. Two meals per day were offered at 12 h intervals. The starch intake was mostly about 2 g/kg bw/meal, except one period with oats (3.9 g starch/kg bw) and with expanded corn (1.4 g/kg bw). Jejunal chyme was postprandially collected 11 times (from 1st to the 11th h after the morning meal for 15 min). Starch was determined polarimetrically. The preileal digestibility of starch was calculated by the marker method (chronic oxide 0.25% DM) and by estimating the total jejunoileal chyme flow during 12 h postprandially extrapolating the sample volume from the 15 min sampling periods. The results of both methods agreed quite well. Preileal digestibility of oat starch (80-90%) was (independent of doses or preparation or of the combination with hay, Table 4) significantly higher than that of whole or crushed corn (30%) or barley (26%). Grinding of corn significantly increased preileal digestibility to 51%, expanding to 90%. The addition of amylase improved digestion of ground corn by 10% (absolute). The preileal digestibility of potato or manioc was less than 10%. Individual factors in the horse (chewing intensity, amylase activity) had also considerable influence on preileal starch digestibility.

Animals↗
PubMed1985

Influence of surfactant-treated starch on the disintegration and dissolution of sulphadiazine tablets.

The effects of treating cassava starch with sodium lauryl sulphate and Polysorbate 80 and the method of incorporating the treated and plain starch as disintegrant on the physical properties of sulphadiazine tablets were investigated. Disintegration and dissolution rates were faster with starch in which surfactant was incorporated in dry state than with starch treated with solution of surfactant. A direct correlation was observed between the Hardness-Friability Index and T90 values. Polysorbate 80-treated starch exhibited a better dissolution profile than SLS-treated starch.

Excipients↗
PubMed1993

Evaluation of starch obtained from Ensete ventricosum as a binder and disintegrant for compressed tablets.

The binding and disintegrant properties of starch obtained from Ensete ventricosum Musaceae have been evaluated. The effect of the starch on the physical properties such as crushing strength, friability and disintegration time of tablets of chloroquine phosphate, dipyrone and paracetamol was compared with tablets prepared with potato starch. The results show that enset starch can be used both as a tablet binder and disintegrant and the indication is that enset starch has a better binding ability and less disintegrating power than potato starch.

Acetaminophen↗
PubMed1992

Location and characterization of genes involved in binding of starch to the surface of Bacteroides thetaiotaomicron.

Previous studies of starch utilization by the gram-negative anaerobe Bacteroides thetaiotaomicron have demonstrated that the starch-degrading enzymes are cell associated rather than extracellular, indicating that the first step in starch utilization is binding of the polysaccharide to the bacterial surface. Five transposon-generated mutants of B. thetaiotaomicron which were defective in starch binding (Ms-1 through Ms-5) had been isolated, but initial attempts to identify membrane proteins missing in these mutants were not successful. We report here the use of an immunological approach to identify four maltose-inducible membrane proteins, which were missing in one or more of the starch-binding mutants of B. thetaiotaomicron. Three of the maltose-inducible proteins were outer membrane proteins (115, 65, and 43 kDa), and one was a cytoplasmic membrane protein (80 kDa). The genes encoding these proteins were shown to be clustered in an 8.5-kbp segment of the B. thetaiotaomicron chromosome. Two other loci defined by transposon insertions, which appeared to contain regulatory genes, were located within 7 kbp of the cluster of membrane protein genes. The 115-kDa outer membrane protein was essential for utilization of maltoheptaose (G7), whereas loss of the other proteins affected growth on starch but not on G7. Not all of the proteins missing in the mutants were maltose regulated. We also detected two constitutively produced proteins (32 and 50 kDa) that were less prominent in all of the mutants than in the wild type. Both of these were outer membrane proteins.

Bacteroides↗
PubMed2001

New regulatory gene that contributes to control of Bacteroides thetaiotaomicron starch utilization genes.

Bacteroides thetaiotaomicron uses starch as a source of carbon and energy. Early steps in the pathway of starch utilization, such as starch binding and starch hydrolysis, are encoded by sus genes, which have been characterized previously. The sus structural genes are expressed only if cells are grown in medium containing maltose or higher oligomers of glucose. Regulation of the sus structural genes is mediated by SusR, an activator that is encoded by a gene located next to the sus structural genes. A strain with a disruption in susR cannot grow on starch but can still grow on maltose and maltotriose. A search for transposon-generated mutants that could not grow on maltose and maltotriose unexpectedly located a gene, designated malR, which regulates expression of an alpha-glucosidase not controlled by SusR. Although a disruption in susR did not affect expression of the malR controlled gene, a disruption in malR reduced expression of the sus structural genes. Thus, MalR appears to participate with SusR in regulation of the sus genes. Results of transcriptional fusion assays and reverse transcription-PCR experiments showed that malR is expressed constitutively. Moreover, multiple copies of malR provided on a plasmid (5 to 10 copies per cell) more than doubled the amount of alpha-glucosidase activity in cell extracts. Our results demonstrate that the starch utilization system of B. thetaiotaomicron is controlled on at least two levels by the regulatory proteins SusR and MalR.

Amino Acid Sequence↗
PubMed2000

Bioavailability of starch and postprandial changes in splanchnic glucose metabolism in pigs.

Changes in splanchnic metabolism in pigs were assessed after meals containing slowly or rapidly digested starch. The pigs were fed a mixed meal containing a "slow" native (n = 5) or a "rapid" pregelatinized (n = 5) cornstarch naturally enriched with [(13)C]glucose. Absorption of [(13)C]glucose was monitored by the arteriovenous difference technique, and infusion of D-[6, 6-(2)H(2)]glucose in the jugular vein was used to calculate the systemic appearance of [(13)C]glucose. Arteriovenous balance data obtained during a 12-h study period showed that the fraction of ingested glucose equivalent appearing as glucose in the portal vein was 49.7 +/- 7.2% for the slow starch and 48.2 +/- 7.5% for the rapid starch (P = 0.86). These values, corrected for the gut extraction of circulating [(13)C]glucose, became 66.4 +/- 5.6 and 65. 3 +/- 5.6%, respectively (P = 0.35). Isotope dilution data indicated that systemic appearance of exogenous [(13)C]glucose represented 62. 9 +/- 7.6 and 67.4 +/- 3.0% of the oral load for slow and rapid starch, respectively (P = 0.68). Arterial glucose utilization by the gut increased from 7.3 +/- 0.9 micromol x kg(-1) x min(-1) before the meal to 8.5 +/- 1.6 micromol x kg(-1) x min(-1) during absorption, independently of the nature of the starch. Thus splanchnic glucose metabolism was unaffected by the nature of starch ingested.

Animals↗
PubMed1988

Starch and glucose oligosaccharides protect salivary-type amylase activity at acid pH.

Salivary-type amylase may significantly contribute to duodenal starch hydrolysis in exocrine pancreatic insufficiency, provided that gastric inactivation does not occur. We investigated the effect of starch and its hydrolytic products, therefore, on salivary amylase activity in vitro at low pH. When incubated at pH 3 in the presence of 1% starch, 56% of the initial activity of amylase purified from saliva remained after 60 min at 37 degrees C compared with only 6% without starch. Similar protection of amylolytic activity was observed using human milk, which also contains a salivary-type amylase. In addition, partially hydrolyzed starch protected salivary amylase activity at pH 3, and purified glucose oligomers ranging in length from two to seven glucose molecules protected amylase in a concentration-dependent manner. Lactose, sucrose, and glucose, however, were ineffective in sparing amylase. Starch protected amylase activity even in the presence of pepsin, and maltotriose conferred striking protection below pH 3. These studies indicate that salivary-type isoamylases are protected in a simulated gastric environment by substrates of amylase as well as its end products of hydrolysis.

Adult↗