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PubMed2001

Reappraisal of the currently prevailing model of starch biosynthesis in photosynthetic tissues: a proposal involving the cytosolic production of ADP-glucose by sucrose synthase and occurrence of cyclic turnover of starch in the chloroplast.

A vast amount of information has accumulated which supports the view that sucrose and starch are end-products of two segregated, yet highly interconnected, gluconeogenic pathways taking place in the cytosol and chloroplast, respectively. However, several lines of experimental evidences indicate that, essentially identical to the case of heterotrophic tissues, starch formation in the photosynthetic tissues may involve the direct import to the chloroplast of cytosolic hexose (C6) units derived from the sucrose breakdown. This evidence is consistent with the idea that synthesis of a sizable pool of ADP-glucose takes place in the cytosol by means of sucrose synthase whereas, basically in agreement with recent investigations dealing with glycogen biosynthesis in bacteria and animals, chloroplastic phosphoglucomutase and ADP-glucose pyrophosphorylase are most likely playing a role in channelling of glucose units derived from the starch breakdown in the chloroplast, thus making up a regulatory starch turnover cycle. According to this new view, we propose that starch production in the chloroplast is the result of a flexible and dynamic mechanism wherein both catabolic and anabolic reactions take place simultaneously in a highly interactive manner. Starch is seen as an intermediate component of a cyclic gluconeogenic pathway which, in turn, is connected with other metabolic pathways. The possible importance of metabolic turnover as a way to control starch production is exemplified with the recently discovered ADP-glucose pyrophosphatase, an enzyme likely having a dual role in controlling levels of ADP-glucose linked to starch biosynthesis and diverting carbon flow towards other metabolic pathways.

Adenosine Diphosphate Glucose↗
PubMed1994

Toward an understanding of the biogenesis of the starch granule. Determination of granule-bound and soluble starch synthase functions in amylopectin synthesis.

Plant starch synthesis can be distinguished from those of bacterial, fungal, and animal glycogen by the presence of multiple elongation (starch synthases) and branching enzymes. This complexity has precluded genetic assignment of functions to the various soluble starch synthases in the building of amylopectin. In Chlamydomonas, we have recently shown that defects in the major soluble starch synthase lead to a specific decrease in the amount of a subset of amylopectin chains whose length ranges between 8 and 40 glucose residues (Fontaine, T., D'Hulst, C., Maddelein, M.-L., Routier, F., Marianne-Pepin, T., Decq, A., Wieruszeski, J. M., Delrue, B., Van Den Koornhuyse, N., Bossu, J.-P., Fournet, B., and Ball, S. G. (1993) J. Biol. Chem. 268, 16223-16230). We now demonstrate that granule-bound starch synthase, the enzyme that was thought to be solely responsible for amylose synthesis, is involved in amylopectin synthesis. Disruption of the Chlamydomonas granule-bound starch synthase structural gene establishes that synthesis of long chains by this enzyme can become an absolute requirement for amylopectin synthesis in particular mutant backgrounds. In the sole presence of soluble starch synthase I, Chlamydomonas directs the synthesis of a major water-soluble polysaccharide fraction and minute amounts of a new type of highly branched granular material, whose structure is intermediate between those of glycogen and amylopectin. These results lead us to propose that the nature of the elongation enzyme conditions the synthesis of distinct size classes of glucans in all starch fractions.

Amylopectin↗
PubMed1976

Starch degradation by the mould Trichoderma viride. I. The mechanism of starch degradation.

The mechanism of starch degradation by the fungus Trichoderma viride was studied in strain CBS 354.44, which utilizes glucose, starch and dextrins but is unable to assimilate maltose. It was shown that the amylolytic enzyme system is completely extracellular, equally well induced by starch, amylose or amylopectin and that it consists mainly of enzymes of the glucoamylase type which yield glucose as the main product of starch hydrolysis. Small amounts of alpha-amylase are produced also. The enzymes produced in starch cultures degrade starch, amylose and amylopectin equally well. Enzyme synthesis in starch media takes place to a considerable extent after exhaustion of the carbon source when maximum growth has been attained. Low-molecular dextrins are degraded by extracellular enzymes of the glucoamylase type. These enzymes are produced in media containing starch or dextrins. Maltotriose is consumed for only one third leaving maltose in the culture filtrate. Maltose is hardly attacked and hardly induces any amylolytic enzyme activity. No stable alpha-glucosidase appears to be produced.

Amylases↗
PubMed1995

Content of starch and sugars and in vitro digestion of starch by alpha-amylase in five minor millets.

Five varieties of minor millets were studied for their amylose, soluble amylose, amylopectin, soluble amylopectin, reducing sugar, total sugar and starch contents. Pure starch was isolated from each variety and the enzymic degradation of starch by porcine pancreatic alpha-amylase were examined with and without gelatinisation. Gelatinised sample of Echinochloa frumentacea (var. K2) showed minimal hydrolysis and gelatinised sample of Panicum miliaceum (var. CO3) showed maximum hydrolysis of starch by porcine pancreatic alpha-amylase. Gelatinised starch was highly susceptible to enzymic digestion when compared to ungelatinised starch. The extent of starch degradation varied from 71 to 85 percent in gelatinised samples and starch degradation in ungelatinised sample varied from 10 to 18 percent.

Amylopectin↗
PubMed1999

Bioavailability of starch in bread rich in amylose: metabolic responses in healthy subjects and starch structure.

OBJECTIVE: This study investigated whether postprandial metabolic responses to bread could be lowered by substituting high amylose maize starch for a part of the flour. DESIGN AND SUBJECTS: Eight healthy subjects consumed test meals of equivalent nutritional composition based on white wheat bread, bread rich in amylose (HAWB) and spaghetti as a breakfast meal. Blood samples were collected to measure insulin and glucose concentration during two hours after consumption. The degree of starch crystallinity was investigated by X-ray diffraction and DSC analysis. RESULTS: HAWB produced low glycaemic (60 +/- 18) and insulinaemic (57 +/- 20) indexes similar to those of spaghetti (83 +/- 46, 61 +/- 16). In vitro amylase hydrolysis of the three foods showed that high amylose content in HAWB significantly lowered starch degradation in bread without affecting hydrolysis kinetics. Addition of amylose in dough increased the resistant starch content of HAWB (14% of dry matter). The resistant starch fraction was mainly composed of crystalline amylose (B-type X-ray diffraction pattern, melting temperature 105 degrees C) attributable to native high amylose maize starch incompletely gelatinised during bread-cooking. CONCLUSIONS: Bread produced by the substitution of high amylose maize starch for a part of wheat flour showed a low glycaemic index. Resistant starch in HAWB corresponded to native crystalline amylose not gelatinised during normal bread-processing conditions.

Adult↗
PubMed1997

ADP-glucose drives starch synthesis in isolated maize endosperm amyloplasts: characterization of starch synthesis and transport properties across the amyloplast envelope.

We recently developed a method of purifying amyloplasts from developing maize (Zea mays L.) endosperm tissue [Neuhaus, Thom, Batz and Scheibe (1993) Biochem. J. 296, 395-401]. In the present paper we analyse how glucose 6-phosphate (Glc6P) and other phosphorylated compounds enter the plastid compartment. Using a proteoliposome system in which the plastid envelope membrane proteins are functionally reconstituted, we demonstrate that this type of plastid is able to transport [14C]Glc6P or [32P]Pi in counter exchange with Pi, Glc6P, dihydroxyacetone phosphate and phosphoenolpyruvate. Glucose 1-phosphate, fructose 6-phosphate and ribose 5-phosphate do not act as substrates for counter exchange. Besides hexose phosphates, ADP-glucose (ADPGlc) also acts as a substrate for starch synthesis in isolated maize endosperm amyloplasts. This process exhibits saturation kinetics with increasing concentrations of exogenously supplied [14C]ADPGlc, reaching a maximum at 2mM. Ultrasonication of isolated amyloplasts greatly reduces the rate of ADPGlc-dependent starch synthesis, indicating that the process is dependent on the intactness of the organelles. The plastid ATP/ADP transporter is not responsible for ADPGlc uptake. Data are presented that indicate that ADPGlc is transported by another translocator in counter exchange with AMP. To analyse the physiology of starch synthesis in more detail, we examined how Glc6P- and ADPGlc-dependent starch synthesis in isolated maize endosperm amyloplasts interact. Glc6P-dependent starch synthesis is not inhibited by increasing concentrations of ADPGlc. In contrast, the rate of ADPGlc-dependent starch synthesis is reduced by increasing concentrations of ATP necessary for Glc6P-dependent starch synthesis. The possible modes of inhibition of ADPGlc-dependent starch synthesis by ATP are discussed with respect to the stromal generation of AMP required for ADPGlc uptake.

Adenine Nucleotides↗
PubMed2000

Reversible binding of the starch-related R1 protein to the surface of transitory starch granules.

Intact starch granules were isolated from leaves of Solanum tuberosum L. (and from Pisum sativum L.), and the patterns of starch-associated proteins were determined by SDS-PAGE. Depending on the pretreatment of the leaves the protein patterns varied: a 160 kDa compound was present in the starch-associated protein fraction when the leaves were darkened and performed net starch degradation. However, following illumination (i.e. during net starch biosynthesis) the 160 kDa protein was recovered almost exclusively in a soluble state. The 160 kDa protein was identified to be the recently described starch-related R1 protein. In in vitro assays recombinant R1 did bind to starch granules isolated from either illuminated or darkened leaves. However, binding to the latter was more effective. It is concluded that, depending upon the metabolic state of the cells, the starch granule surface changes and thereby affects binding of the R1 protein.

Molecular Weight↗
PubMed2002

Adaptation to the digestion of nutrients of a starch diet or a non-starch polysaccharide diet in group-housed pregnant sows.

A trial was conducted with twenty group-housed pregnant sows to study the adaptation in nutrient digestibility to a starch-rich diet or a diet with a high level of fermentable non-starch polysaccharides (NSP) during a time period of 6 weeks. The starch-rich diet was primarily composed of wheat, peas and tapioca, whereas soya bean hulls and sugar beet pulp, which both are highly fermentable NSP sources, were used to formulate the NSP-rich diet. The starch-rich diet and the NSP-rich diet were formulated to contain different levels of starch (298 vs. 78 g/kg) and fermentable NSP (100 vs. 300 g/kg), but a similar level of net energy (NE) (8.36 MJ/kg). The trial consisted of a 1-week adaptation period followed by a 5-week collection period. Weekly apparent faecal digestibilities of dry matter (DM), crude protein (CP), crude fat, ash and NSP were measured by using the acid-insoluble ash marker method. Apparent faecal digestibilities of DM and organic matter (OM) of both diets were similar. Faecal digestibility of CP and crude fat was lower (p < 0.001) whereas that of NSP was higher (p < 0.001) for sows that received the NSP-rich diet. Calculated NE values of both diets were similar. Sows fed the NSP-rich diet produced faeces that contained a lower (p < 0.001) DM content compared with sows that were fed with the starch-rich diet. The quantity of dry faeces was the same on both diets, therefore total faeces production (as-is basis) was higher (p < 0.01) for the sows fed the NSP-rich diet. During the 5-week collection period, no changes were observed in the digestibility of DM, OM and NSP in the NE value of the diets. Digestibilities of CP and fat, however, were lower in week 1 (p < 0.05) compared with weeks 2-5 for both diets. The DM content of the faeces and the quantity of dry faeces did not change from weeks 1-5. Diet by time interaction was not observed for any of the response variables indicating that sows adapt as quickly to a diet with a high level of fermentable NSP as to a starch-rich diet. The present trial shows that, with regard to digestibility of nutrients, pregnant sows completely adapt to a NSP-rich diet (i.e., NSP from sugar beet pulp) in 2 weeks and that the time period necessary to adapt to a starch-rich diet or a diet with a high level of fermentable NSP is similar.

Adaptation, Physiological↗
PubMed1996

All medium starches are not the same: influence of the degree of hydroxyethyl substitution of hydroxyethyl starch on plasma volume, hemorrheologic conditions, and coagulation.

BACKGROUND: After the application of high volumes of high-molecular-weight starch (hetastarch), bleeding complications have repeatedly been observed. Later studies showed that the application of medium-molecular-weight starch led to far fewer disturbances of the blood coagulation system. However, the relationships among the degree of hydroxyethyl substitution, the rate of degradation, and the average in vivo molecular weight have not been investigated. STUDY DESIGN AND METHODS: A 10-day hemodilution treatment (n = 20) was carried out using two medium-molecular-weight hydroxyethyl starches (HES) with a degree of hydroxyethyl substitution of 0.5 and 0.62, respectively (10% HES 200 was used for a substitution of 0.5 and 6% HES 200 for a substitution of 0.62). After a loading dose of 500 mL was administered, 1000 mL of HES was infused daily for 4 days, and then 500 mL was infused daily for 6 days. RESULTS: The more highly substituted starch was broken down more slowly and eliminated renally. This resulted in a higher intravascular molecular weight than for the less highly substituted HES (120 vs. 84 kDa) and a greater increase in serum concentration (20.3 vs. 9.0 mg/mL). Initially, the more highly substituted 6-percent HES had a lesser effect on plasma volume (p < 0.01). Because of HES accumulation, there was no longer a significant difference between the starches by the end of treatment, even though a higher dose of the 10-percent low-substitution starch was infused. Six-percent HES caused an increase in plasma viscosity (+9%, p < 0.01) that was due to an accumulation of macromolecules. Ten-percent HES 200/0.5 had no effect on the coagulation system beyond the dilution effect. Six-percent HES, on the other hand, led to an acquired von Willebrand syndrome during the course of the 10-day therapy. Factor VIII function was reduced by 72.2 percent, von Willebrand ristocetin cofactor by 61.3 percent, and von Willebrand factor antigen by 64 percent (p < 0.01). CONCLUSION: It is the intravascular and not the initial (in vitro) molecular weight that determines the properties of HES. Especially after repeated administration, a high degree of hydroxyethyl substitution leads to an accumulation of macromolecules that affect hemorrheologic measures and the coagulation system just as adversely as high-molecular-weight starch does. Depending on the degree of substitution, medium-molecular-weight starches can have widely differing properties.

Blood Coagulation↗
PubMed2004

Antisense downregulation of the barley limit dextrinase inhibitor modulates starch granule size distribution, starch composition and amylopectin structure.

The barley protein limit dextrinase inhibitor (LDI), structurally related to the alpha-amylase/trypsin inhibitor family, is an inhibitor of the starch debranching enzyme limit dextrinase (LD). In order to investigate the function of LDI, and the consequences for starch metabolism of reduced LDI activity, transgenic barley plants designed to downregulate LDI by antisense were generated. Homozygous antisense lines with reduced LDI protein level and activity were analysed and found to have enhanced free LD activity in both developing and germinating grains. In addition the antisense lines showed unpredicted pleiotropic effects on numerous enzyme activities, for example, alpha- and beta-amylases and starch synthases. Analysis of the starch showed much reduced numbers of the small B-type starch granules, as well as reduced amylose relative to amylopectin levels and reduced total starch. The chain length distribution of the amylopectin was modified with less of the longer chains (>25 units) and enhanced number of medium chains (10-15 units). These results suggest an important role for LDI and LD during starch synthesis as well as during starch breakdown.

Amylopectin↗
PubMed1991

Small intestinal starch digestion in steers: effect of various levels of abomasal glucose, corn starch and corn dextrin infusion on small intestinal disappearance and net glucose absorption.

Eight Holstein steers (four at 300 kg, four at 406 kg) fitted with an elevated carotid artery, hepatic portal and mesenteric venous catheters, and abomasal and ileal cannulas were used in several 4 x 4 Latin square experiments to evaluate small intestinal starch digestion. They were fed alfalfa hay at 1.5% of BW and abomasally infused with water or glucose, corn starch or corn dextrin (one carbohydrate per Latin square) at 20, 40 or 60 g/h, with subsequent determination of small intestinal disappearance and net portal glucose absorption. Increasing the amount of all three carbohydrates infused abomasally increased the amount of carbohydrate disappearing in the small intestine. Increased infusion of glucose caused a continual increase (linear, P less than .01) in net glucose absorption, whereas net glucose absorption for starch and dextrin was maximal at the 20 g/h infusion (quadratic, P less than .05). With the 60 g/h infusion, 94% of the glucose but only 38% of starch and 29% of small intestinal dextrin disappearance could be accounted for as net glucose absorption, leaving a large portion of starch and dextrin disappearance unaccounted for. Of the infused starch and dextrin passing the ileum, 5.8 and 7.3%, respectively, was unpolymerized glucose, indicating that, at least in the distal small intestine, complete starch hydrolysis exceeded the capacity for glucose disappearance. It is concluded that only about 35% of the raw corn starch disappearing in the steer's small intestine resulted in net portal glucose absorption.

Animals↗
PubMed2007

Two high-amylose maize starches with different amounts of resistant starch vary in their effects on fermentation, tissue and digesta mass accretion, and bacterial populations in the large bowel of pigs.

Four groups of young pigs (n 6) were fed a diet containing 50% maize starch as either a highly digestible waxy starch (control; 0% amylose) or one of three resistant starch (RS) diets, namely a high-amylose maize starch (HAMS; 85% amylose), this starch subjected to hydrothermal treatment (HTHAMS; 85% amylose), or a blend of HAMS and HTHAMS included in equal amounts, for 21 d. Food intake and live weight at the end of the study were similar among the four groups. Ileal starch digestibility was lower in pigs fed the three RS diets but was greater for HAMS(88%) than for HTHAMS (70%; P<0.05). Faecal output and large bowel digesta mass, and concentrations and pools of individual and total SCFA were higher (by about two- to threefold; all P<0.05) and digesta pH lower (by about 1 unit, all P<0.001) in pigs fed either HAMS or HTHAMS compared to the controls. These differences in biomarkers were seen along the length of the large bowel. Colon length was 0.5-0.9 m longer (19-35%) in pigs fed the high-RS diets relative to those fed the highly digestible starch diet (P<0.05). Faecal and proximal colonic lactobacilli and bifidobacteria numbers were higher (by 1 and 3 log units; P< 0.05) in pigs fed the HAMS or HTHAMS diets. Although both high-amylose starches promoted fermentation throughout the large bowel, the data suggest that the effects of HTHAMS may be more pronounced in the distal region compared to those of HAMS.

Amylose↗
PubMed2003

Microbial starch-binding domains as a tool for targeting proteins to granules during starch biosynthesis.

Modification of starch biosynthesis pathways holds an enormous potential for tailoring granules or polymers with new functionalities. In this study, we explored the possibility of engineering artificial granule-bound proteins, which can be incorporated in the granule during biosynthesis. The starch-binding domain (SBD)-encoding region of cyclodextrin glycosyltransferase from Bacillus circulans was fused to the sequence encoding the transit peptide (amyloplast entry) of potato granule-bound starch synthase I (GBSS I). The synthetic gene was expressed in the tubers of two potato cultivars (cv. Kardal and cv. Karnico) and one amylose-free (amf) potato mutant. SBDs accumulated inside starch granules, not at the granule surface. Amylose-free granules contained 8 times more SBD (estimated at ca. 1.6% of dry weight) than the amylose-containing ones. No consistent differences in physicochemical properties between transgenic SBD starches and their corresponding controls were found, suggesting that SBD can be used as an anchor for effector proteins without having side-effects. To test this, a construct harbouring the GBSS I transit peptide, the luciferase reporter gene, a PT-linker, and the SBD (in frame), and a similar construct without the linker and the SBD, were introduced in cv. Kardal. The fusion protein accumulated in starch granules (with retainment of luciferase activity), whereas the luciferase alone did not. Our results demonstrate that SBD technology can be developed into a true platform technology, in which SBDs can be fused to a large choice of effector proteins to generate potato starches with new or improved functionalities.

Amino Acid Sequence↗
PubMed2004

Effect of fermentation on the starch digestibility, resistant starch and some physicochemical properties of sorghum flour.

The effect of natural fermentation of Tabat sorghum cultivar (Sorghum bicolor L. Moench) at 37 degrees C for up to 36 h on pH, titratable acidity, starch digestibility, resistant starch and total starch was studied. The pH of the fermenting dough decreased sharply with a concomitant increase in the titratable acidity. In vitro starch digestibility markedly increased as a result of fermentation, while resistant starch and total starch decreased. Results showed that iodine absorption capacity increased during fermentation. Fermented sorghum had more soluble starch and swelling power at 100 degrees C than at 85 degrees C.

Chemical Phenomena↗
PubMed2003

Production and physicochemical characterization of resistant starch type III derived from pea starch.

Smooth pea starch was used for the production of physiological important resistant starch type III. For reduction of the molecular weight of the starch, different strategies including enzymatic debranching and acid hydrolysis (lintnerization), were tested to obtain an optimal starting material for retrogradation. The resulting polymer chain lengths were analyzed by high-performance anion-exchange chromatography. Temperature regimes and starch concentrations in gel were optimized during the retrogradation with the aim to obtain a high yield of resistant starch. Optimal conditions led to resistant starch contents up to 74%. The products were thermostable and showed no loss of resistant structures after autoclaving. The peak temperatures of the thermal transition were at approximately 147 degrees C. The resulting resistant starch products are suitable for the generation of functional foods.

Chemical Phenomena↗
PubMed1998

Overexpression of pyrophosphatase leads to increased sucrose degradation and starch synthesis, increased activities of enzymes for sucrose-starch interconversions, and increased levels of nucleotides in growing potato tubers.

Overexpression of inorganic pyrophosphatase (PPase) from Escherichia coli in the cytosol of plants (ppa 1 plants) leads to a decrease of inorganic pyrophosphate (PPi; U. Sonnewald, 1992, Plant J 2: 571-581). The consequences for sucrose-starch interconversions have now been studied in growing potato (Solanum tuberosum L. cv. Desirée) tubers. Sucrose is degraded via sucrose synthase and UDP-glucose pyrophosphorylase in growing tubers, and it was expected that the low PPi in the ppa 1 transformants would restrict the mobilisation of sucrose and conversion to starch. Over-expression of PPase resulted in an accumulation of sucrose and UDP-glucose, and decreased concentrations of hexose phosphates and glycerate-3-phosphate in growing ppa 1 tubers. Unexpectedly, the rate of degradation of [14C] sucrose was increased by up to 30%, the rate of starch synthesis was increased, and the starch content was increased by 20-30% in ppa 1 tubers compared to wild-type tubers. Reasons for this unexpectedly efficient conversion of sucrose to starch in the ppa 1 tubers were investigated. (i) The transformed tubers contained increased activities of several enzymes required for sucrose-starch interconversions including two- to three-fold more sucrose synthase and 60% more ADP-glucose pyrophosphorylase. They also contained 30-100% increased activities of several glycolytic enzymes and amylase, increased protein, and unaltered or slightly decreased starch phosphorylase, acid invertase and mannosidase. (ii) The transformants contained higher pools of uridine nucleotides. As a result, although the UDP-glucose pool is increased two- to threefold, this does not lead to a decrease of UTP or UDP. (iii) The transformants contained twofold larger pools of ATP and ADP, and ADP-glucose was increased by up to threefold. In stored ppa 1 tubers, there were no changes in the activities of glycolytic enzymes, and nucleotides did not increase. It is concluded that in growing tubers PPi has a wider-significance than just being an energy donor for specific reactions in the cytosol. Increased rates of PPi hydrolysis also affect general aspects of cell activity including the levels of nucleotides and protein. Possible ways in which PPi hydrolysis could affect these processes are discussed.

Carbon Radioisotopes↗
PubMed2005

Structure function relationships of transgenic starches with engineered phosphate substitution and starch branching.

Potato tuber starch was genetically engineered in the plant by the simultaneous antisense suppression of the starch branching enzyme (SBE) I and II isoforms. Starch prepared from 12 independent lines and three control lines were characterised with respect to structural and physical properties. The lengths of the amylopectin unit chains, the concentrations of amylose and monoesterified phosphate were significantly increased in the transgenically engineered starches. Size exclusion chromatography with refractive index detection (SEC-RI) indicated a minor decrease in apparent molecular size of the amylose and the less branched amylopectin fractions. Differential scanning calorimetry (DSC) revealed significantly higher peak temperatures for gelatinisation and retrogradation of the genetically engineered starches whereas the enthalpies of gelatinisation were lower. Aqueous gels prepared from the transgenic starches showed increased gel elasticity and viscosity. Principle component analysis (PCA) of the data set discriminated the control lines from the transgenic lines and revealed a high correlation between phosphate concentration and amylopectin unit chain length. The PCA also indicated that the rheological characteristics were primarily influenced by the amylose concentration. The phosphate and the amylopectin unit chain lengths had influenced primarily the pasting and rheological properties of the starch gels.

Amylopectin↗
PubMed2002

Starch phosphorylation: a new front line in starch research.

Starch is the primary energy reserve in higher plants and is, after cellulose, the second most abundant carbohydrate in the biosphere. It is also the most important energy source in the human diet and, being a biodegradable polymer with well-defined chemical properties, has an enormous potential as a versatile renewable resource. The only naturally occurring covalent modification of starch is phosphorylation. Starch phosphate esters were discovered a century ago but were long regarded as a curiosity, receiving little attention. Indeed, the mechanism for starch phosphorylation remained completely unknown until recently. The starch-phosphorylating enzyme is an alpha-glucan water dikinase. It is now known that starch phosphorylation plays a central role in starch metabolism.

Amylopectin↗