Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “STARCH”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,513 records · Page 84Linked to original sources
PubMed1993

Dietary non-starch polysaccharides interact with cholesterol and fish oil in their effects on plasma lipids and hepatic lipoprotein receptor activity in rats.

Male rats were fed the non-starch polysaccharides pectin, methylcellulose or guar gum with corn oil or with 60% of the corn oil replaced by fish oil. They were also fed these diets with or without cholesterol (+ cholic acid). Plasma total cholesterol concentration was higher overall in rats fed cholesterol and lower in those fed fish oil or fish oil + cholesterol. Plasma triacylglycerols were lower in rats fed fish oil with or without cholesterol. Hepatic LDL receptor activity was higher overall in rats fed fish oil or fish oil + cholesterol than in those fed cholesterol. Liver HDL receptor was lower overall in rats fed fish oil or cholesterol. Type of non-starch polysaccharide influenced these dietary effects so that in cholesterol-fed rats plasma cholesterol was highest in those fed methylcellulose, intermediate in those fed guar gum and in those fed pectin was unchanged from concentrations in rats fed pectin without cholesterol. Fish oil feeding lowered plasma cholesterol concentration in rats fed pectin or methylcellulose but not in those fed guar gum. Plasma triacylglycerols were lower in rats fed fish oil and all three non-starch polysaccharides, but concentrations were similar in rats fed pectin + fish oil + cholesterol and in those fed pectin. In rats fed methylcellulose + cholesterol and any non-starch polysaccharide + fish oils, HDL receptor activity was uniformly lower than in rats fed pectin, methylcellulose or guar gum. Low density lipoprotein receptor activity was higher in rats fed pectin + fish oil or pectin + fish oil + cholesterol than in rats fed pectin.

Animals↗
PubMed1995

Amylopectin starch promotes the development of insulin resistance in rats.

Starches that are high in amylopectin are digested and absorbed more quickly than starches with a high amylose content and produce larger postprandial glucose and insulin responses. The aim of this study was to test the hypothesis that feeding rats a diet containing quickly digested starch could promote insulin resistance. Sprague-Dawley rats were fed either a high amylopectin or high amylose diet (two 10-g meals per day), and insulin sensitivity was assessed after 9 wk by intravenous glucose tolerance test (IVGTT). In the rats fed the high amylopectin diet, glucose tolerance was significantly lower (P < 0.05) and the insulin response to IVGTT was twice as high as in rats fed the high amylose diet (P < 0.05). A second study using Wistar rats investigated the time course of these changes. Differences in the insulin response to the IVGTT were not evident at 4 wk but began to emerge at 8 wk, and by 12 wk the insulin response was 100% greater in rats fed the high amylopectin diet (P < 0.05) than in those fed the high amylose diet. In addition, basal plasma insulin concentration was higher in rats fed the high amylopectin diet (P < 0.05). There were no differences, however, in glucose tolerance at any time point. The results suggests that quickly digested starch promotes the development of insulin resistance in rats. The relatively slow time course resembles the normal development of insulin resistance in humans.

Amylopectin↗
PubMed1986

Accumulation of starch in roots and foliage of loblolly pine (Pinus taeda L.): effects of season, site and fertilization.

Accurate predictions of stand response to nitrogen fertilization require a better understanding of the plant processes associated with stand nutrition. This study examined the relationship between stand nutrition and starch accumulation in roots and foliage of loblolly pine (Pinus taeda L.). A field study was located on the lower Coastal Plain of North Carolina on four sites of differing soil types. Stands of 8-year-old trees were fertilized with nitrogen (225 kg ha(-1)) or nitrogen plus phosphorus (225 kg N ha(-1) + 75 kg P ha(-1)) in 1981. Roots and foliage were collected from five trees per plot at six sampling dates from July 1983 through January 1985 and analyzed for starch. Starch concentrations showed seasonal fluctuations, with levels generally highest in early spring prior to budbreak. Root starch concentrations were lowest in autumn, whereas foliar concentrations were lowest in winter.

Journal Article↗
PubMed2002

Functional interactions between heterologously expressed starch-branching enzymes of maize and the glycogen synthases of Brewer's yeast.

Starch-branching enzymes (SBEs) catalyze the formation of alpha(1-->6) glycoside bonds in glucan polymers, thus, affecting the structure of amylopectin and starch granules. Two distinct classes of SBE are generally conserved in higher plants, although the specific role(s) of each isoform in determination of starch structure is not clearly understood. This study used a heterologous in vivo system to isolate the function of each of the three known SBE isoforms of maize (Zea mays) away from the other plant enzymes involved in starch biosynthesis. The ascomycete Brewer's yeast (Saccharomyces cerevisiae) was employed as the host species. All possible combinations of maize SBEs were expressed in the absence of the endogenous glucan-branching enzyme. Each maize SBE was functional in yeast cells, although SBEI had a significant effect only if SBEIIa and SBEIIb also were present. SBEI by itself did not support glucan accumulation, whereas SBEIIa and SBEIIb both functioned along with the native glycogen synthases (GSs) to produce significant quantities of alpha-glucan polymers. SBEIIa was phenotypically dominant to SBEIIb in terms of glucan structure. The specific branching enzyme present had a significant effect on the molecular weight of the product. From these data we suggest that SBEs and GSs work in a cyclically interdependent fashion, such that SBE action is needed for optimal GS activity; and GS, in turn, influences the further effects of SBE. Also, SBEIIa and SBEIIb appear to act before SBEI during polymer assembly in this heterologous system.

1,4-alpha-Glucan Branching Enzyme↗
PubMed1992

Transport Processes and Corresponding Changes in Metabolite Levels in Relation to Starch Synthesis in Barley (Hordeum vulgare L.) Etioplasts.

Intact etioplasts with an intactness of 85% and with a cytosolic and a mitochondrial contamination of less than 10% were isolated from 8-d-old dark-grown barley (Hordeum vulgare) leaves. These plastids contained starch equivalent to 21.5 mumol of glucose per mg protein. From various likely precursors applied to isolated etioplasts, only dihydroxyacetone phosphate (DHAP) had significant effects on metabolite levels and on the internal ATP/ADP ratio. The concentration dependence of DHAP uptake exhibited saturation characteristics with half saturation at 0.36 mm DHAP and a maximal velocity of 6.6 mumol mg(-1) of protein h(-1). The transport was significantly inhibited by inorganic phosphate, pyridoxal-5'-phosphate, and 4,4'-diisothiocyano-2,2'-stilbenedisulfonate. The rate of glucose-6-phosphate uptake was much lower and not saturable up to a concentration of 10 mm. Exogenously applied [(14)C]DHAP was incorporated into starch at a rate of 0.14 mumol of DHAP mg(-1) of protein h(-1). Enzyme activities required to convert DHAP into starch were found to be present in etioplasts. Furthermore, enzymes generating ATP from DHAP for ADPglucose synthesis were also detected. Finally, a scheme is presented suggesting DHAP uptake to serve both as carbon skeleton and as energy source for starch synthesis, mediated by a translocator with properties similar to those of the triose phosphate translocator from chloroplasts.

Journal Article↗
PubMed1996

Synthesis and Turnover of Cell-Wall Polysaccharides and Starch in Photosynthetic Soybean Suspension Cultures.

Soybean (Glycine max [L.] Merr.) suspension cultures grown under photoautotrophic and photomixotrophic (1% sucrose) culture conditions were used in 14CO2 pulse-chase experiments to follow cell-wall polysaccharide and starch biosynthesis and turnover. Following a 30-min pulse with 14CO2, about one-fourth of the 14C of the photoautotrophic cells was incorporated into the cell wall; this increased to about 80% during a 96-h chase in unlabeled CO2. Cells early in the cell culture cycle (3 d) incorporated more 14C per sample and also exhibited greater turnover of the pectin and hemicellulose fractions as shown by loss of 14C during the 96-h chase than did 10- and 16-d cells. When the chase occurred in the dark, less 14C was incorporated into the cell wall because of the cessation of growth and higher respiratory loss. The dark effect was much less pronounced with the photomixotrophic cells. Even though the cell starch levels were much lower than in leaves, high 14C incorporation was found during the pulse, especially in older cells. The label was largely lost during the chase, indicating that starch is involved in the short-term storage of photosynthate. Thus, these easily labeled and manipulated photosynthetic cells demonstrated extensive turnover of the cell-wall pectin and hemicellulose fractions and starch during the normal growth process.

Journal Article↗
PubMed1999

Expression of the granule-bound starch synthase I (Waxy) gene from snapdragon is developmentally and circadian clock regulated

The granule-bound starch synthase I (GBSSI or waxy) enzyme catalyzes one of the enzymatic steps of starch synthesis. This enzyme is responsible for the synthesis of amylose and is also involved in building the final structure of amylopectin. Little is known about expression of GBSSI genes in tissues other than storage organs, such as seeds, endosperm, and tuber. We have isolated a gene encoding the GBSSI from snapdragon (Antirrhinum majus). This gene is present as a single copy in the snapdragon genome. There is a precise spatial and developmental regulation of its expression in flowers. GBSSI expression was observed in all floral whorls at early developmental stages, but it was restricted to carpel before anthesis. These results give new insights into the role of starch in later reproductive events such as seed filling. In leaves the mRNA level of GBSSI is regulated by an endogenous circadian clock, indicating that the transition from day to night may be accompanied by abolition of expression of starch synthesis genes. This mechanism does not operate in sink tissues such as roots when grown in the dark.

Journal Article↗
PubMed1976

Starch degradation in the cotyledons of germinating lentils.

Starch, total amylolytic and phosphorylase activities were determined in lentil cotyledons during the first days of germination. Several independent criteria show that the amylolytic activity is due mainly to an amylase of the alpha type. Starch is degraded slowly in the first days; during this time, alpha- and beta-amylase activity are very low, while phosphorylase increases and reach a peak on the 3rd day. On the 4th day, there is a more rapid depletion of starch which coincides with an increase in alpha-amylase activity. By polyacrylamide gel electrophoresis of the crude starch-degrading enzyme, five bands were obtained: one phosphorylase, three alpha-amylases, and one beta-amylase. Based on their heat lability or heat stability, two sets of alpha-amylase seem to exist in lentil cotyledons.

Journal Article↗
PubMed1977

Free sugars in relation to starch accumulation in developing rice grain.

The changes in sugars (water-soluble carbohydrates) were studied in the developing grain of rice (Oryza sativa L., variety IR28 and IR29) in relation to the role of these sugars as precursors of ADP glucose in starch accumulation. The levels of total sugars, total reducing sugars and free glucose, sucrose and other nonreducing sugars, maltooligosaccharides, and total and nonsucrosyl fructose followed closely the changes in the rate of starch accumulation, in both IR28 and 29; the peak value occurred 9 days after flowering. The level of soluble carbohydrates remained high in the caryopsis and also in milled rice after starch accumulation, suggesting that the supply of sugar precursors does not limit starch accumulation in the rice grain. Because of a higher level of reducing sugars, the level of free sugars in the grain of waxy rice IR29 was higher than that of nonwaxy IR28.

Journal Article↗
PubMed1979

Starch-synthesizing Enzymes in the Endosperm and Pollen of Maize.

Two mutations, amylose-extender and waxy, which affect the proportion of amylose and amylopectin of starch synthesized in the endosperm of maize (Zea mays L.) seeds, are also expressed in the pollen. However, most mutations that affect starch synthesis in the maize endosperm are not expressed in the pollen. In an attempt to understand the nonconcordance between the endosperm and pollen, extracts of mature pollen grains were assayed for a number of the enzymes possibly implicated in starch synthesis in the endosperm. Sucrose synthetase (sucrose-UDP glucosyl transferase, EC 2.4.1.13) activity was not detectable in either mature or immature pollen grains of nonmutant maize, but both bound and soluble invertase (EC 3.2.1.26) exhibited much greater specific activity (per milligram protein) in pollen extracts than in 22-day-old endosperm extracts. Phosphorylase (EC 2.4.1.1) activity was also higher in pollen than in endosperm extracts. ADP-Glucose pyrophosphorylase (EC 2.7.7.27) activity was much lower in pollen than endosperm extracts, but mutations that drastically reduced ADP-glucose pyrophosphorylase activity in the endosperm (brittle-2 and shrunken-2) did not markedly affect enzymic activity in the pollen. Specific activities of other enzymes implicated in starch synthesis were similar in endosperm and pollen extracts.

Journal Article↗
PubMed1979

Subcellular localization of the starch degradative and biosynthetic enzymes of spinach leaves.

The subcellular localization of the starch biosynthetic and degradative enzymes of spinach leaves was carried out by measuring the distribution of the enzymes in a crude chloroplast pellet and soluble protein fraction, and by the separation on sucrose density gradients of intact organelles, chloroplasts, peroxisomes, and mitochondria of a protoplast lysate. ADP-Glucose pyrophosphorylase, starch synthase, and starch-branching enzymes are quantitatively associated with the chloroplasts. The starch degradative enzymes amylase, R-enzyme (debranching activity), phosphorylase, and D-enzyme (transglycosylase) are observed both in the chloroplast and soluble protein fractions, the bulk of the degradative enzyme activities reside in the latter fraction. Chromatography of a chloroplast extract on diethylaminoethyl-cellulose resolves the R- and D-enzymes from amylase and phosphorylase activities although the two latter enzyme activities coeluted. The digestion pattern of amylase with amylopectin as a substrate indicates an endolytic activity but displays properties unlike the typical alpha-amylase as isolated from endosperm tissue.

Journal Article↗
PubMed1979

Isolation and purification of leaf starch components.

A procedure was developed for the separation and purification of amylose and amylopectin isolated from cotton leaves. Cotton leaves were homogenized in 0.02 molar phosphate buffer at pH 7.0 containing HgCl(2) plus toluene. Crude starch granules were collected by centrifugation and partially purified by treating with acetone and toluene. The starch granules were then dispersed in dimethylsulfoxide and precipitated with ethyl alcohol. The precipitate was suspended in boiling water. Amylose was separated from amylopectin and cell wall particles on a Sepharose 2B column and further purified with thymol and butanol. Amylopectin was then separated from the colloidal cell wall contaminants by its specific interaction with concanavalin A. Purities of starch components were verified by specific biochemical and enzymic tests in addition to their iodine-binding capacity. This procedure should also be suitable for purification of starch components from other plant sources.

Journal Article↗
PubMed1981

Measurement of Metabolites Associated with Nonaqueously Isolated Starch Granules from Immature Zea mays L. Endosperm.

Starch granules with associated metabolites were isolated from immature Zea mays L. endosperm by a nonaqueous procedure using glycerol and 3-chloro-1,2-propanediol. The soluble extract of the granule preparation contained varying amounts of neutral sugars, inorganic phosphate, hexose and triose phosphates, organic acids, adenosine and uridine nucleotides, sugar nucleotides, and amino acids. Based on the metabolites present and on information about translocators in chloroplast membranes, which function in transferring metabolites from the chloroplast stroma into the cytoplasm, it is suggested that sucrose is degraded in the cytoplasm, via glycolysis, to triose phosphates which cross the amyloplast membrane by means of a phosphate translocator. It is further postulated that hexose phosphates and sugars are produced from the triose phosphates in the amyloplast stroma by gluconeogenesis with starch being formed from glucose 1-phosphate via pyrophosphorylase and starch synthase enzymes. The glucose 1-phosphate to inorganic phosphate ratio in the granule preparation was such that starch synthesis by phosphorylase is highly unlikely in maize endosperm.

Journal Article↗
PubMed1982

Effects of the relative extrachloroplastic concentrations of inorganic phosphate, 3-phosphoglycerate, and dihydroxyacetone phosphate on the rate of starch synthesis in isolated spinach chloroplasts.

The effect of external inorganic phosphate (Pi) on starch synthesis in isolated spinach (Spinacia oleracea American Hybrid No. 424) chloroplasts in the presence of millimolar concentrations of 3-phosphoglycerate (PGA) and/or dihydroxyacetone phosphate (DAP) was examined. Whereas CO(2) fixation was relatively constant as the ratio of the external phosphate to the PGA + DAP varied from 1:3 to 3:1, starch synthesis varied from 17% to 2% of the CO(2) fixation rate. With DAP alone, maximal starch synthesis was about 10% of the CO(2) fixation rate. The data demonstrate that the Pi/(PGA + DAP) ratio in the cytoplasm of plant cells could serve to regulate the flow of newly fixed carbon into starch without alterations in the rate of CO(2) fixation.

Journal Article↗
PubMed1983

Changes in Starch Formation and Activities of Sucrose Phosphate Synthase and Cytoplasmic Fructose-1,6-bisphosphatase in Response to Source-Sink Alterations.

Short term experiments were conducted with vegetative soybean plants (Glycine max L. Merr. ;Ransom' or ;Arksoy') to determine whether sourcesink manipulations, which rapidly changed the ;demand' for sucrose and partitioning of photosynthetically fixed carbon into starch, were associated with alterations in activities of sucrose-P synthase and/or cytoplasmic fructose-1,6-bisphosphatase in leaf extracts. When demand for sucrose from a particular source leaf was increased by defoliation of other source leaves, starch accumulation was restricted and activities of both enzymes were markedly enhanced. When demand for sucrose from source leaves was limited by excision, starch accumulation in the detached leaves was increased while activity of sucrose-P synthase declined sharply. The consistent responsiveness of sucrose-P synthase activity to changes in demand for sucrose supports the contention that regulation of sucrose-P synthase is an integral component of the system which controls sucrose biosynthesis and partitioning of carbon between starch and sucrose biosynthesis in the light.

Journal Article↗
PubMed1983

Starch synthesis in shriveled and plump triticale seeds.

Seven lines of triticale (X Triticosecale Wittmack) with either shriveled or plump seed characteristics were planted in the field, and seed developmental changes in weight, starch content, the activity of starch biosynthetic and degradative enzymes, and ATP content were studied in three consecutive years in Oregon. Experimental results varied among genotypes and with growing environment, but overall indicated that: (a) amylase activity was higher in shriveled lines, but was not directly synchronized with the occurrence of shriveling at later stages of seed formation; (b) ADP-glucose starch synthase contributed to starch accumulation in triticale, but it appeared not to be associated with shriveledness as no stage-related changes were observed; and (c) ADP-glucose pyrophosphorylase activity was 2- to 3-fold higher in plump lines than that of shriveled lines, indicating that this enzyme may play an important role in the degree of plumpness or stach accumulation of triticale seeds.

Journal Article↗
PubMed1985

Partial purification and characterization of granule-bound starch synthases from normal and waxy maize.

The granule-bound starch-synthases from normal and waxy maize kernels have been solubilized, partially purified, and characterized. Two broad categories of starch synthases were revealed with representatives in the soluble phase and also on granules from both normal and waxy maize though the activity associated with granules from waxy was small. Data for native molecular weights, kinetic parameters, and immunological relatedness are used to demonstrate that the granule-bound isozymes from normal maize are different from the soluble enzymes. These distinct granule-bound enzymes are missing in waxy maize granules and a further novel form of starch synthase is revealed. These findings are discussed in relation to the type of starch produced in tissue affected by the waxy mutation.

Journal Article↗
PubMed1986

Glyphosate inhibits photosynthesis and allocation of carbon to starch in sugar beet leaves.

Application of glyphosate (N-[phosphonomethyl] glycine) to exporting leaves of sugar beet (Beta vulgaris, L.) during the day lowered stomatal conductance and carbon fixation. Allocation of newly fixed carbon to foliar starch accumulation was nearly completely inhibited, being decreased by the same amount as net carbon fixation. In contrast, decreasing net carbon fixation in untreated leaves by lowering CO(2) concentration caused starch accumulation to decrease, but only in the same proportion as net carbon fixation. Shikimate level increased 50-fold in treated leaves but the elevated rate of carbon accumulation in shikimate was only 4% of the decrease in the rate of starch accumulation. Application of steady state labeling with (14)CO(2) to exporting leaves confirmed the above changes in carbon metabolism, but revealed no other major daytime differences in the (14)C-content of amino acids or other compounds between treated and control leaves. Less (14)C accumulated in treated leaves because of decreased fixation, not increased export. The proportion of newly fixed carbon allocated to sucrose increased, maintaining export at the level in control leaves. Returning net carbon exchange to the rate before treatment restored starch accumulation fully and prevented a decrease in export during the subsequent dark period.

Journal Article↗