Actions of porcine pancreatic and Bacillus subtilis alpha-amylases and Aspergillus niger glucoamylase on phosphorylated (1--4)-alpha-D-glucan

Physicochemical properties of potato starches manufactured in Hokkaido factories

Potato starch is an important agricultural product in Hokkaido, the northernmost island of Japan, with output of around 0.18 million tons/year. The present investigation was conducted to evaluate the physicochemical properties of potato starch samples manufactured in 10 factories in Hokkaido. The starch samples were analyzed for pasting properties by rapid visco analyzer (RVA), gelatinization properties by differential scanning calorimetry (DSC), color components, and minerals, amylose, and resistant starch (RS) contents. The phosphorus and potassium contents of potato starches averaged 746 ppm and 681 ppm, ranging from 669 to 835 ppm and from 481 to 803 ppm, respectively. Relatively wide ranges were noted in the contents of sodium (35-134 ppm), magnesium (50-121 ppm), and calcium (34-164 ppm). RVA analysis revealed clear differences in peak viscosity (PV) and breakdown (BD) among starch samples examined. Higher contents of divalent cations, magnesium, and calcium, were associated with lower values of PV and BD, whereas the phosphorus content did not affect PV and BD. The differences in amylose content, DSC gelatinization properties and color components as well as RS content in raw starch were not large.

Slower Fermentation Rate of Potato Starch Relative to High-amylose Cornstarch Contributes to the Higher Proportion of Cecal Butyrate in Rats

This study aimed to examine the mechanism for differential effects of low- (LPPS) and high-phosphorus (HPPS) potato starches and high-amylose cornstarch (HACS) on rat cecal fermentation, the n-butyrate proportion in particular. In ileorectostomized rats, the in vivo resistant starch (RS) contents were determined to be 66% (LPPS), 66% (HPPS) and 36% (HACS), but the carbohydrate/nitrogen (C/N) ratios of the ileal digesta were comparable among the respective starch diets. In intact rats fed diets including similar amounts of RS, the cecal n-butyrate proportions in the LPPS- and HPPS-fed rats were equally higher than in the HACS-fed rats. The cecal starch contents were fivefold greater in the LPPS- and HPPS-fed rats than in the HACS-fed rats. The results suggest that potato starches and HACS are not equivalent n-butyrate producers in the rat cecum and that the slower fermentation rate of potato starches relative to HACS might be responsible for the higher n-butyrate proportion.

Factors affecting the digestibility of raw and gelatinized potato starches

The enzymatic digestibilities of raw and gelatinized starches in various potato starches, as well as sweet potato, cassava, and yam starches, were estimated, along with other starch properties, such as the phosphorus content, median granule size, and rapid visco analyzer (RVA) pasting properties. Furthermore, correlation coefficients were calculated between the hydrolysis rates (HR) by amylase and other starch quality parameters. A larger granule size was closely associated with a lower HR in raw starch, while the HR in gelatinized starch did not correlate with the median granule size. An increase in phosphorus content resulted in a definitely lower HR in raw starch and tended to decrease the HR in gelatinized starch for the composite of potato and other starches. In contrast, no correlation coefficients of the phosphorus content with the HRs in raw and gelatinized starches were observed within potato starches. Starches with higher peak viscosity and breakdown showed a lower HR in raw starch, while few or no effects of these RVA parameters on the HR in gelatinized starch were observed for the composite of potato and other starches or among potato starches, respectively.

Potato pulps lowered the serum cholesterol and triglyceride levels in rats

In our previous study, we demonstrated that retrograded starch, a kind of resistant starch, of beans reduced serum lipid levels in rats. In this study, we examined whether retrograded starch in potato pulps could reduce serum lipid concentrations. Rats were given diets containing 15 g of retrograded starch in potato pulps from the Benimaru potato (BM) or Hokkaikogane potato (HK) in a 100 g diet for 4 wk. At the 4th week, the total cholesterol level in the serum in the BM group and serum triglyceride (TG) level in the HK group were significantly lower than those in the control group. In the BM group, the contents of fecal bile acids were significantly higher than those in the control group. On the other hand, in the HK group, the hepatic mRNA level of fatty acid synthase (FAS) was significantly lower than that in the control group. The FAS mRNA level correlated with the mRNA level of sterol regulatory element-binding protein-1c (SREBP-1c), a regulator of expression of FAS, positively. These results suggested that BM pulp promoted the excretion of bile acids, which resulted in a low concentration of serum cholesterol. On the other hand, HK pulp inhibited the synthesis of fatty acids at the mRNA levels of FAS and SREBP-1c, which might lead to a reduction of the serum TG level.

Phosphorylation of C6- and C3-positions of glucosyl residues in starch is catalysed by distinct dikinases

Glucan, water dikinase (GWD) and phosphoglucan, water dikinase (PWD) are required for normal starch metabolism. We analysed starch phosphorylation in Arabidopsis wild-type plants and mutants lacking either GWD or PWD using (31)P NMR. Phosphorylation at both C6- and C3-positions of glucose moieties in starch was drastically decreased in GWD-deficient mutants. In starch from PWD-deficient plants C3-bound phosphate was reduced to levels close to the detection limit. The latter result contrasts with previous reports according to which GWD phosphorylates both C6- and C3-positions. In these studies, phosphorylation had been analysed by HPLC of acid-hydrolysed glucans. We now show that maltose-6-phosphate, a product of incomplete starch hydrolysis, co-eluted with glucose-3-phosphate under the chromatographic conditions applied. Re-examination of the specificity of the dikinases using an improved method demonstrates that C6- and C3-phosphorylation is selectively catalysed by GWD and PWD, respectively.

Enzymatic degradation and electrospray tandem mass spectrometry as tools for determining the structure of cationic starches prepared by wet and dry methods

Cationic starches from various semi-technical processes, two 'wet' (slurry and paste modification) and two 'dry' procedures (dry modification and extrusion), each type in a DS range from 0.03 to 0.1, were investigated by electrospray ionisation mass spectrometry (ESIMS) and tandem mass spectrometry (ESIMS2) after enzymatic degradation with alpha-amylase and subsequent glucoamylase digestion. For comparison, chemically derived cationic oligosaccharides were also analysed by ESIMS. The cationisation pattern in the glucosyl units was analysed by GLC after methanolysis, permethylation and Hofmann elimination. Results from ESIMS are discussed and interpreted with respect to enzyme susceptibility, monomer composition and physical properties of the different types of cationic starches.

Production of highly phosphorylated glycopolymers by expression of R1 in Escherichia coli

The possible involvement of the starch bound R1 protein from potato (Solanum tuberosum L.) in the phosphorylation of starch was investigated by functional expression and characterisation of R1 in Escherichia coli. By expression of R1 in E. coli it is shown that it is possible to produce glycopolymers, e.g., glycogen, with an increased degree of phosphate substitution. The expression of R1 in E. coli resulted in a sixfold increase in glycogen bound phosphate and in an increased accumulation of glycogen leading to a glycogen excess (gex) phenotype. There was an overall shift in the unit-chain length of the isolated glycogen towards smaller degrees of polymerisation. The pleiotropic effects on the glycogen biosynthetic and amylolytic enzyme activities was investigated and showed an increase in ADPglucose pyrophosphorylase activity, as well as a decrease in exo-amylolytic activity. These results are discussed in relation to starch phosphorylation and a possible role of R1 in this respect.

Actions of Aspergillus oryzae alpha-amylase, potato phosphorylase, and rabbit muscle phosphorylase a and b on phosphorylated (1----4)-alpha-D-glucan

Aspergillus oryzae alpha-amylase [(1----4)-alpha-D-glucan glucanohydrolase, EC 3.2.1.1] produced O-(6-phosphoryl-alpha-D-glucopyranosyl)-(1----4)-O-alpha-D-glucopyran osy l-(1----4)-D-glucopyranose (6(3)-phosphorylmaltotriose) and O-alpha-D-glucopyranosyl-(1----4)-O-(3-phosphoryl-alpha-D-glucopyranosyl )- (1----4)-O-alpha-D-glucopyranosyl-(1----4)-D-glucopyranose (3(3)-phosphorylmaltotetraose) from potato starch upon exhaustive hydrolysis. These products indicate that the enzyme hydrolyses the same linkages in the vicinity of the 6-phosphorylated residue as porcine-pancreatic alpha-amylase, but hydrolyses different linkages in the vicinity of the 3-phosphorylated residue when compared with B. subtilis and pancreatic alpha-amylases. Potato phosphorylase [(1----4)-alpha-D-glucan:orthophosphate alpha-D-glucosyltransferase, EC 2.4.1.1] and rabbit muscle phosphorylase a and b were unable to by-pass the phosphorylated D-glucosyl residue of 6-phosphorylated (1----4)-alpha-D-glucan, leaving three D-glucosyl residues attached to the 6-phosphorylated residue on the non-reducing side.

Porcine-pancreatic alpha amylase hydrolysis of substrates containing 6-deoxy-D-glucose and 6-deoxy-6-fluoro-D-glucose and the specificity of subsite binding

Hydrolysis of 6-deoxyamylose and mono-6-deoxy-6-fluorocyclomaltoheptaose by porcine-pancreatic alpha amylase produces low-molecular-weight modified products, which have been analyzed by chemical and chromatographic techniques. Results for both substrates show that modified D-glucose and two isomers of modified maltoses are produced in the enzyme reaction. In addition, the formation of maltoses modified in the nonreducing residue is more favored than the formation of maltoses modified in the reducing residue. These results indicate that productive binding of 6-fluoro- and 6-deoxy-D-glucose residues is permitted at subsites 1 through 4 of the amylase-active site but that binding of these modified residues may be less favorable at subsite 3, the subsite at which catalytic attack occurs.

The effect of substrate modification on porcine pancreatic alpha-amylase subsite binding: hydrolysis of substrates containing 2-deoxy-D-glucose and 2-amino-2-deoxy-D-glucose

Modified alpha-D-(1----4)-glucans containing a small proportion of 14C-labeled 2-deoxy-D-glucose or 2-amino-2-deoxy-D-glucose were examined as substrates for porcine pancreatic alpha-amylase (PPA). Cyclomaltoheptaose containing single 2-deoxy-D-glucose residues, synthesized by incubation of 2-deoxyglucosylglycogen with cyclomaltodextrin glucanotransferase in the presence of Triton X-100, was hydrolyzed by PPA to produce 2-deoxy-D-glucose; two isomers of 2-deoxymaltose, and a mixture of modified maltotrioses. These results indicate that 2-deoxymaltose, and a mixture of modified maltotrioses. These results indicate that 2-deoxy-D-glucose may be productively bound at all five subsites of the PPA active site. Reaction kinetics and the distribution of products formed suggest, however, that productive binding of the modified residue does not occur readily at the point of catalytic attack (subsite 3) and that the preferred position of hydrolysis of modified substrates may be different from that of unmodified substrates. Results of PPA hydrolysis of glycogen containing [14C]-2-amino-2-deoxy-D-glucose showed that a modified trisaccharide and a modified disaccharide were the smallest substituted products formed. Analysis of these products indicated that they did not contain modified residues at their reducing ends. Formation of the observed 2-amino-2-deoxy-maltooligosaccharides is consistent with a scheme where productive binding of 2-amino-2-deoxy-D-glucose is allowed at subsites 1, 2, 4, and 5, but not at subsite 3, the subsite at which hydrolysis occurs.

The effect of substrate modification on binding of porcine pancreatic alpha amylase: hydrolysis of modified amylose containing D-allose residues

A modified amylose containing 10% of tritiated D-allose residues has been hydrolyzed by porcine pancreatic alpha amylase (PPA). This reaction produced a number of radioactive oligosaccharides of low molecular weight, including modified mono-, di-, and tri-saccharides, as well as larger products. Analysis of these products by chemical and enzymic methods identified D-allose, two isomers of modified maltose, and isomers of modified maltotriose. These results may be interpreted in terms of current PPA models to indicate that D-allose residues may be productively bound at all five subsites of the active site of the enzyme. The distribution of modified residues in these products, however, further suggests that productive binding of D-allose at the subsite where catalytic attack occurs (subsite 3) is less favorable than binding of D-glucose. These results are compared with results of a series of PPA substrates having modifications at C-3 and at other positions. Trends observed in enzyme hydrolysis of these modified substrates reflect factors that contribute to PPA catalysis, with respect to steric, electronic, and hydrogen-bonding interactions between enzyme and substrate.

Porcine pancreatic alpha-amylase hydrolysis of hydroxyethylated amylose and specificity of subsite binding

Hydrolysis of partially hydroxyethylated amylose by porcine pancreatic alpha-amylase gives rise to a number of hydroxyethylated di-, tri-, and tetrasaccharides, as well as larger products. No modified monosaccharides were detected. The structures of the products containing two to four D-glucose residues have been analyzed by chromatographic and enzymatic techniques. In no instance were these oligosaccharides modified in the reducing-end residue. The location of hydroxyethylated glucose residues within the oligosaccharides has been interpreted in terms of the ability of that (hydroxyethyl)glucose to bind productively at each of the five subsites of the enzyme active site. Results indicate that subsite 3, the subsite at which catalytic attack occurs, is especially sensitive to changes in the substrate and that unmodified glucose is required for productive binding at this subsite. Other subsites specifically allow binding of some (hydroxyethyl)glucose isomers, but not others. Hydroxyethylation is permitted at C-2, C-3, and C-6 for residues bound at subsite 1 and is permitted at C-6 and possibly at C-2 and C-3 for residues bound at subsite 5. However, substitution is permitted only at C-3 and C-6 for binding at subsite 2 and at C-2 and C-3 for binding at subsite 4.