Biosynthesis of Sucrose and Sucrose-Phosphate by Sugar Beet Leaf Extracts

Abstract

Cardini and coworkers (6) reported as one part of a plant materials survey that "negative or non-reproducible results" were obtained in sucrose synthesis studies with sugar beet leaves and roots. They stated that these results "may be attributed to the presence of interfering enzymes". Burma and Mortimer (5), using isotopic tracer techniques, reported the synthesis of sucrose by sugar beet leaf homogenates when fructose-6-phosphate and uridine diphosphoglucose (UDPG) were present. They demonstrated that sucrose-phosphate was formed and assumed that it was subsequently dephosphorvlated by phosphatase to sucrose. No sucrose synthesis occurred when fructose or fructose-1,6-diphosphate and UDPG were added to sugar beet leaf homogenates. Burma and Mortimer stated that their experiments with sugar beet leaves eliminated Leloir and Cardini's (11) first enzyme mechanism demonstrated with wheat germ, which was the interaction of UDPG and fructose for the direct formation of sucrose plus pyro-phosphate. This paper presents data showing that the assumption of Burma and Mortimer that only sucrose-phosphate is synthesized directly does not seem to be correct. Rather, it shows that sugar beet leaf tissue contains enzyme systems for the direct synthesis of sucrose as well as sucrose-phosphate through UDPG and fructose and UDPG and fructose-6-phosphate, respectively.