Sorbose sucrose phosphorylase

Sucrose phosphorylase exhibits a very high degree of specificity for the glucose portion of its substrates, but it reacts mth a number of glycosyl acceptors in addition to phosphate and fructose. The enzyme from P. saccharophUa, but not from P. putrefadens, will react with sorbose. 

This enzyme is very specific it does not react with sorbose, fructose phosphates, glucose, or any other compound tested in place of fructose, and glucose-l-phosphate cannot replace UDPG. Unlike the case of sucrose phosphorylase, the equilibrium of this reversible reaction favors sucrose synthesis, and the presence of this enzyme in the cells of higher plants implicates this reaction in sucrose synthesis. 

The high energy bond in a substituted glucosyl phosphate might be important for sucrose synthesis. The equilibrium constant for reaction (i) was shown to be 2 to 8 at 37° and pH 7.4, indicating that this reaction favors sucrose formation. As for sucrose phosphorylase, L-sorbose, D-xylulose and D-rhamnulose acted as acceptors to give the corresponding disaccharides °. 

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