Exchange reactions sucrose phosphorylase

Maltose phosphorylase cannot carry out a similar reaction. The P exchange reaction of sucrose phosphorylase is accounted for by a double-displacement mechanism where E = E-glucose ... 

Isotope exchange studies yield information about the existence of reaction intermediates. Sucrose phosphorylase provides an example of the isotope exchange studies. This enzyme cataljrzes the foUowing exchanges, each carried out in the absence of the second substrate ... 

It will be observed that in this, as well as in the phosphorolysis reaction, the enzyme acts as glucose donor and glucose acceptor to its substrates, and is able to catalyze the exchange of an ester bond for a glyco-sidic bond. The role of sucrose phosphorylase in the reversible phosphorolysis of sucrose can thus be considered as a summation of the two reactions. 

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. 

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