A study of the phosphorylated products of sfiort-term 

 photosynthesis in C^^02 led to the discovery of a sucrose 

 phosphate (93). The "hexose monophosphates" produced 

 during photosynthesis in C^'^02 were treated with an inver- 

 tase-free phosphatase preparation and subjected to paper 

 chromatography. Although in most cases there were only 

 minute traces of sucrose formed by this treatment, in sugar 

 beet (5 minutes in Ci''02) there was an appreciable quantity. 

 It was identified by cochromatography and enzymic hydroly- 

 sis to glucose and fructose. 



When this "hexose monophosphate" sample was sub-^ 

 jected to chromatography in ^butanol: picric acid: water, ra- 

 dioactive areas corresponding to glucose-6-phosphate, fruc- 

 tose-6-phosphate, sedoheptulose and mannose phosphates, 

 and sucrose phosphate were obtained. The sucrose phosphate 

 gave sucrose on phosphatase treatment, and on acid hydrolysis 

 glucose and fructose phosphate were produced. The latter 

 did not cochromatograph with fructose-6-phosphate. 



It appeared that in sucrose synthesis in green plants 

 there are two possible mechanisms. Glucose- 1 -phosphate 

 might react with fructose- 1 -phosphate to give sucrose phos- 

 phate, which would be dephosphorylated to sucrose. Alter- 

 natively, sucrose phosphate synthesis might be envisaged to 

 occur through uridine diphosphate glucose (15), which be- 

 comes labeled shortly before sucrose in kinetic experiments 

 with €^^^02 (18). The uridine diphosphate glucose may be 

 formed from glucose- 1 -phosphate by a UDPG pyrophosphory- 

 lase (reaction 15, Table 3). This pathway is shown in Figure 

 8 along with other pathways that may very likely occur dur- 

 ing photosynthesis of carbohydrates from CO2. 



Leloir and Cardini (85) have isolated from wheat germ 

 what appears to be two systems, one that catalyzes the reac- 

 tion of fructose plus UDPG to give sucrose plus UDP, and 

 a second that catalyzes the reaction UDPG plus fructose-6- 

 phosphate to give sucrose phosphate plus UDP. Burma and 

 Mortimer (94) have reported that with excised sugar beet 

 leaves and leaf homogenates radioactive UDPG and sucrose 



54 



