Phosphate, inorganic sucrose phosphorylase

Sucrose phosphorylase can then be regarded as a rather versatile transglucosidase, capable of exchanging glycosidic and ester bonds and of donating D-glucose to a variety of substrates such as ketoses, an aldose, inorganic phosphate and arsenate. 

Recently Kuriki and coworkers succeeded in producing glucose-1-phosphate in situ during the enzymatic polymerization of amylose. By using sucrose phosphorylase or cellobiose phosphorylase, the monomer was produced during the polymerization from inorganic phosphate and sucrose or cellobiose, respectively [119-121]. 

Katayama Y. Enzymatic inorganic phosphate with use of sucrose phosphorylase and phosphoglucomutase. Clin Chem 1992 38 512-5. 

A number of polysaccharides can also be prepared using non-Leloir glycosyl transferases. Maltooligomers could be polymerized by potato phosphorylase (PPh, E.C. 2.4.1.1). The activated glucose 1-phosphate in this scheme was generated in situ from sucrose and inorganic phosphate by the action of sucrose phosphorylase (SPh, E.C. 2.4.1.7, Scheme 21) (49). 

When a mixture of UDPG and D-fructose is subjected to the reaction of enz3nne preparations from these plant sources in the presence of inorganic phosphate buffer at pH 7.0, a nonreducing disaccharide, identified as sucrose, is formed. The equilibrium constant, Ky for this reaction at 37°C was found to be between 2 and 8, and the AF was estimated to be approximately —1000 cal. as compared to +1770 cal. for the sucrose phosphorylase reaction. In contrast to the sucrose phosphorylase reaction, the equilibrium of the reaction starting with UDPG and D-fructose is in favor of sucrose synthesis. 

The evidence for the double function of the enzyme was obtained from the fact that when P -labeled inorganic phosphate and nonradioactive a-D-glucose 1-phosphate are added to sucrose phosphorylase preparations... 

L. mesenteroides also contains a sucrose phosphorylase. However, since it has been demonstrated that sucrose is converted to dextran by dex-transucrase in the absence of a detectable quantity of inorganic phosphate and that the enzyme does not form polysaccharide from glucose-l-phos-phate, it is clear that phosphorylase is not involved in dextran synthesis. The evidence indicates that the dextransucrase acts by a direct transfer of glucose units. The reaction appears to involve the substitution of a 1,6-glucosidic linkage for a glucose-fructose bond and can be represented by. the following equation ... 

The reaction is essentially an exchange of hypoxanthine for phosphate, and is analogous to the phosphorolysis of glycogen and sucrose. For this reason, the enzyme has been termed nucleoside phosphorylase. It can also catalyze an exchange between ribose-l-phosphate and inorganic phosphate. This was shown by incubating ribose-l-phosphate with P in the presence of the enzyme and subsequently isolating radioactive ribose-l-phosphate. With arsenate, an irreversible arsenolysis of the nucleoside results. 

When cultures or enzyme preparations of N. perfiava are allowed to act on a-D-glucose-l-phosphate, some amylopolysaccharide is produced, indicating the presence of a phosphorylase. However, the amylosucrase can be distinguished from the bacterial phosphorylase by its stability to heat and by the fact that the synthesis of the polysaccharide from sucrose is not suppressed in high concentration of inorganic phosphate. The synthetic reaction proceeds without a noticeable lag period, suggesting that primer material, if needed, is present in the preparations. Although there is no direct evidence for this, the fact that the formation of polysaccharide is completely inhibited in the presence of traces of salivary amylase indicates that a primer may be required. 

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