Glucose sucrose phosphorylase reaction with

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 fact that sucrose can be synthesized from -D-glucose 1-phosphate and D-fructose is consistent with the evidence presented by Isbell and Pigman 172) and Gottschalk 173) that D-fructose exists as an equilibrium mixture of the pyranose and furanose forms. The total system of sucrose synthesis can be represented by the equation (Fig. 4) which includes the equilibrium reaction of the two ring forms of D-fructose. The occurrence of D-fructose in the sucrose molecule as D-fructofuranose is an indication that sucrose phosphorylase is specific for the furanose configuration of that ketose 17A, 175),... 

It was at this state of knowledge that an incidental observation with extracts of C. kluy-veri led to a development which played a significant role in elucidating the mechanism of CoA action. It was observed that arsenate inhibited the ability of extracts to catalyze the oxidation of butyrate, as well as the reduction of acetyl-P and acetate to butyrate. The inhibition was ultimately explained by the fact that arsenate stimulated the enzymic hydrolysis of acetyl-P [reaction (18)]. By analogy to the postulated role of arsenate in the hydrolysis of glucose-l-P by sucrose phosphorylase,< > it was proposed that the arsenolysis of acetyl-P could be the result of a reversible transfer of the acetyl moiety to an acetyl acceptor, x , catalyzed by a phosphotransacetylase [reaction (21)]. 

In green tissues Smith (320) showed sucrose rather than starch to be formed in brief photosynthesis, and in their experiments with C H)s Calvin and Benson (69) found that sucrose became labeled when no labeled glucose or fructose could be detected. The conclusion was drawn that sucrose arose from G-6-P and F-6-P, rather than from the free sugars. Although the synthesis of sucrose carried out by bacterial enzymes described by Hassid el al. (149) resembles the phosphorylase reactions described above, a different mechanism of sucrose synthesis is found in plants. Recent work by Buchanan (57) and by Leloir and his co-workers (73,223,224) has shown the following reactions leading to sucrose synthesis ... 

E3 UDP-sugar phosphorylase. E4 pyrophosphatase. (Below) Synthesis of 6 -deoxy-6 -fluorosucrose. El, sucrose synthetase E2, pyruvate kinase E3, UDP-glucose pyrophosphorylase E4, pyrophosphatase. All enzymes (150 U each) are co-immobilized in polyacrylamide gel. The reactions are carried out in triethanolamine buffer (50 mM) containing MgCl2 (10 mM) with pH being controlled at 7.5 by addition of IN NaOH. The 500-mL reaction mixture contains glucose-... 

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