Regulatory Properties of the ADP-Glucose Pyrophosphorylase of the Blue-Green Bacterium Synechococcus 6301

Prospective bacterial and fungal sources of hyaluronic acid: A review

The unique biological and rheological properties make hyaluronic acid a sought-after material for medicine and cosmetology. Due to very high purity requirements for hyaluronic acid in medical applications, the profitability of streptococcal fermentation is reduced. Production of hyaluronic acid by recombinant systems is considered a promising alternative. Variations in combinations of expressed genes and fermentation conditions alter the yield and molecular weight of produced hyaluronic acid. This review is devoted to the current state of hyaluronic acid production by recombinant bacterial and fungal organisms.

Sucrose accumulation in salt-stressed cells of agp gene deletion-mutant in cyanobacterium Synechocystis sp PCC 6803

The agp gene encoding the ADP-glucose pyrophosphorylase is involved in cyanobacterial glycogen synthesis and glucosylglycerol formation. By in vitro DNA recombination technology, a mutant with partial deletion of agp gene in the cyanobacterium Synechocystis sp. PCC 6803 was constructed. This mutant could not synthesize glycogen or the osmoprotective substance glucosylglycerol. In the mutant cells grown in the medium containing 0.9 M NaCl for 96 h, no glucosylglycerol was detected and the total amount of sucrose was 29 times of that of in wild-type cells. Furthermore, the agp deletion mutant could tolerate up to 0.9 M salt concentration. Our results suggest that sucrose might act as a similar potent osmoprotectant as glucosylglycerol in cyanobacterium Synechocystis sp. PCC 6803.

Alteration of inhibitor selectivity by site-directed mutagenesis of Arg(294) in the ADP-glucose pyrophosphorylase from Anabaena PCC 7120

Previous alanine scanning mutagenesis of ADP-glucose pyrophosphorylase from Anabaena PCC 7120 indicated that Arg(294) plays a role in inhibition by orthophosphate [J. Sheng, J. Preiss, Biochemistry 36 (1997) 13077]. In this study, analysis of several site-directed mutants in the presence of different metabolic effectors showed that the primary inhibitor for two of the mutant proteins, R294A and R294Q, was no longer orthophosphate but rather NADPH, which was a reversal in the pattern of inhibitor selectivity from the wild-type. Despite the differences in charge and size, analysis of the purified R294K, R294E, and R294Q mutant enzymes demonstrated similar decreases in orthophosphate affinity as the R294A mutant, while most of the other kinetic values were similar to those reported for the wild-type. All these results suggest that the positive charge of Arg(294) is not specifically involved in orthophosphate binding and that it is important in determining inhibitor selectivity.

Involvement of arginine residues in the allosteric activation and inhibition of Synechocystis PCC 6803 ADPglucose pyrophosphorylase

ADPglucose pyrophosphorylase (EC 2.7.7.27) from the cyanobacterium Synechocystis PCC 6803 was desensitized to the effects of allosteric ligands by treatment with the arginine reagent, phenylglyoxal. Enzyme modification by phenylglyoxal resulted in inactivation when the enzyme was assayed under 3P-glycerate-activated conditions. There was little loss of the catalytic activity assayed in the absence of activator. Pi, 3P-glycerate, and pyridoxal-P were able to protect the enzyme from inactivation, whereas substrates gave minimal protection. The protective effect exhibited by Pi and 3P-glycerate was dependent on effector concentration. MgCl2 enhanced the protection afforded by 3P-glycerate. The enzyme partially modified by phenylglyoxal was more resistant to 3P-glycerate activation and Pi inhibition than the unmodified form. Vmax at saturating 3P-glycerate concentrations and the apparent affinity of the enzyme toward Pi were decreased upon phenylglyoxal modification. Incorporation of labeled phenylglyoxal into the enzyme was proportional to the loss of activity. Pi and 3P-glycerate nearly completely prevented incorporation of the reagent to the protein. Results suggest that one arginine residue per mol of enzyme subunit is involved in the binding of allosteric effector in the cyanobacterial ADPglucose pyrophosphorylase.

Regulatory and Structural Properties of the Cyanobacterial ADPglucose Pyrophosphorylases

ADPglucose pyrophosphorylase (EC 2.7.7.27) has been purified from two cyanobacteria: the filamentous, heterocystic, Anabaena PCC 7120 and the unicellular Synechocystis PCC 6803. The purification procedure gave highly purified enzymes from both cynobacteria with specific activities of 134 (Synechocystis) and 111 (Anabaena) units per milligram protein. The purified enzymes migrated as a single protein band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis with molecular mass corresponding to 53 (Synechocystis) and 50 (Anabaena) kilodaltons. Tetrameric structures were determined for the native enzymes by analysis of gel filtrations. Kinetic and regulatory properties were characterized for the cyanobacterial ADPglucose pyrophosphorylases. Inorganic phosphate and 3-phosphoglycerate were the most potent inhibitor and activator, respectively. The Synechocystis enzyme was activated 126-fold by 3-phosphoglycerate, with saturation curves exhibiting sigmoidicity (A(0.5) = 0.81 millimolar; n(H) = 2.0). Activation by 3-phosphoglycerate of the enzyme from Anabaena demonstrated hyperbolic kinetics (A(0.5) = 0.12 millimolar; n(H) = 1.0), having a maximal stimulation of 17-fold. I(0.5) values of 95 and 44 micromolar were calculated for the inhibition by inorganic phosphate of the Synechocystis and Anabaena enzyme, respectively. Pyridoxal-phosphate behaved as an activator of the cyanobacterial enzyme. It activated the enzyme from Synechocystis nearly 10-fold with high apparent affinity (A(0.5) = 10 micromolar; n(H) = 1.8). Phenylglyoxal modified the cyanobacterial enzyme by inactivating the activity in the presence of 3-phosphoglycerate. Antibody neutralization experiments showed that anti-spinach leaf (but not anti-Escherichia coli) ADPglucose pyrophosphorylase serum inactivated the enzyme from cyanobacteria. When the cyanobacterial enzymes were resolved on sodium dodecyl sulfate- and two-dimensional polyacrylamide gel electrophoresis and probed with Western blots, only one protein band was recognized by the anti-spinach leaf serum. The same polypeptide strongly reacted with antiserum prepared against the smaller spinach leaf 51 kilodalton subunit, whereas the anti-54 kilodalton antibody raised against the spinach subunit reacted weakly to the cyanobacterial subunit. Regulatory and immunological properties of the cyanobacterial enzyme are more related to the higher plant than the bacterial enzyme. Despite this, results suggest that the ADPglucose pyrophosphorylase from cyanobacteria is homotetrameric in structure, in contrast to the reported heterotetrameric structures of the higher plant ADPglucose pyrophosphorylase.

Observations on chloroplast starch content and synthesis in the intertidal marine alga Codium fragile (Suringar) Hariot

A marked seasonal response was observed in the starch content of chloroplasts of Codium fragile sampled between November 1983 and November 1984. Chloroplast starch uniformly increased throughout the life-cycle of this alga, reaching a maximum in the summer months of approx. 5 mg glucose equivalents/10⁹ plastids when C. fragile was in the reproductive phase. Chloroplast starch content was found to be inversely proportional to the concentration of stromal phosphate, decreasing linearly from 5 to 2 mg glucose equivalents/10⁹ plastids over a range of stromal phosphate values of 0·75-1·5 μmol PO₄ /10⁹ plastids. Similarly, the net amount of starch synthesized over 3 h by isolated chloroplasts increased linearly with respect to initial chloroplast starch content. These observations are discussed in relation to the regulation of starch synthesis by variations in the stromal P₁ : PGA ratio.

Effect of inorganic phosphate, 3-phosphoglycerate and glucose-6-phosphate on net starch synthesis by isolated chloroplasts of Codium fragile (Suringar) Hariot

Net starch synthesis isolated chloroplasts of Codium fragile appears to be regulated in a similar manner to that of vascular plants. Exogenous 10 mol m^-3 PGA stimulated net starch synthesis at 200 μmol m^-2 s ^-1 (PPFD) by approx. 69%, whilst 10 mol m^-3 P₁ not only inhibited synthesis but also promoted net starch degradation. However, unlike vascular plant chloroplasts, 10 mol m^-3 G6P was found to stimulate net starch synthesis by approx. 52% under the same conditions. This apparent difference in response to exogenous G6P is discussed in relation to the operation of the P₁ -G6P translocator in chloroplasts of this species.

Regulation of ADP-Glucose Pyrophosphorylase from Chlorella vulgaris

ADP-glucose pyrophosphorylase was partially purified from Chlorella vulgaris 11h. 3-Phosphoglycerate activated the enzyme by lowering the Michaelis constant for glucose-1-phosphate (from 0.97 to 0.36 millimolar in the presence of 2 millimolar phosphoglycerate) and ATP (from 0.23 to 0.10 millimolar), as well as increasing the V(max). Saturation curves for 3-phosphoglycerate were hyperbolic and the activator concentration at half V(max) value for 3-phosphoglycerate was 0.41 millimolar either in the presence or absence of phosphate. Phosphate inhibited the enzyme in a competitive manner with respect to glucose-1-phosphate, but did not affect the Michaelis constant value for ATP. 3-Phosphoglycerate changed neither the inhibitor concentration at half V(max) value of 1.0 millimolar for phosphate nor the hyperbolic inhibition kinetics for phosphate. The enzyme required divalent cations for its activity. The activation curves for Mn(2+) and Mg(2+) were highly sigmoidal. The activator concentration at half V(max) values for Mn(2+) and Mg(2+) were 2.8 and 3.7 millimolar, respectively. With optimal cations, the Michaelis constant values for ATP-Mn and ATP-Mg were 0.1 and 0.4 millimolar, respectively.

Pyrophosphorylases in Solanum tuberosum: II. CATALYTIC PROPERTIES AND REGULATION OF ADP-GLUCOSE AND UDP-GLUCOSE PYROPHOSPHORYLASE ACTIVITIES IN POTATOES

Pyrophosphorylytic kinetic constants (S(0.5), V(max)) of partially purified UDP-glucose- and ADP-glucose pyrophosphorylases from potato tubers were determined in the presence of various intermediary metabolites. The S(0.5) of UDP-glucose pyrophosphorylase for UDP-glucose (0.17 millimolar) or pyrophosphate (0.30 millimolar) and the V(max) were not influenced by high concentrations (2 millimolar) of these substances. The most efficient activator of ADP-glucose pyrophosphorylase was 3-P-glycerate (A(0.5) = 4.5 x 10(-6) molar). The S(0.5) for ADP-glucose and pyrophosphate was increased 3.5-fold (0.83 to 0.24 millimolar) and 1.8-fold (0.18 to 0.10 millimolar), respectively, with 0.1 millimolar 3-P-glycerate while the V(max) was increased nearly 4-fold. The magnitude of 3-P-glycerate stimulation was dependent upon the integrity of key sulfhydryl groups (-SH) and pH. Oxidation or blockage of -SH groups resulted in a marked reduction of enzyme activity. Stimulations of 3.1-, 2.9-, 4.8-, and 9.5-fold were observed at pH 7.5, 8.0, 8.5, and 9.0, respectively, in the presence of 3-P-glycerate (2 millimolar). The most potent inhibitor of ADP-glucose pyrophosphorylase was orthophosphate (I(0.5) = 8.8 x 10(-5). molar). This inhibition was reversed with 3-P-glycerate (1.2 x 10(-4) molar), resulting in an increased I(0.5) value of 1.5 x 10(-3) molar. Likewise, orthophosphate (7.5 x 10(-4) molar) caused a decrease in the activation efficiency of 3-P-glycerate (A(0.5) from 4.5 x 10(-6) molar to 6.7 x 10(-5) molar). The significance of 3-P-glycerate activation and orthophosphate inhibition in the regulation of alpha-glucan biosynthesis in Solanum tuberosum is discussed.

The purification and characterization of ADP-glucose pyrophosphorylase A from developing maize seeds

ADPglucose pyrophosphorylase A (ATP:alpha-D-glucose-1-phosphate adenylyltransferase, EC 2.7.7.27) from developing maize (Zea mays) endosperm was purified 129 fold to apparent homogeneity. The molecular weight estimated by gel filtration and by polyacrylamide gel electrophoresis was 375 000 and 400 000, respectively. The preparation gave a single protein band after SDS-polyacrylamide gel electrophoresis suggesting a monomer mol. wt. of 96 000. It was concluded that ADPglucose pyrophosphorylase A in maize endosperm is a tetramer of four similar molecular weight subunits. Values for the Km for glucose 1-phosphate and ATP were 3.8 . 10(-5) and 1.8 . 10(-4) M, respectively (using the homogeneous preparation).