sucrose-phosphate synthase, putative, glycosyltransferase domain. This family consists of the N-terminal regions, or in some cases the entirety, of bacterial proteins closely related to plant sucrose-phosphate synthases (SPS). The C-terminal domain (TIGR02471), found with most members of this family, resembles both bona fide plant sucrose-phosphate phosphatases (SPP) and the SPP-like domain of plant SPS. At least two members of this family lack the SPP-like domain, which may have binding or regulatory rather than enzymatic activity by analogy to plant SPS. This enzyme produces sucrose 6-phosphate and UDP from UDP-glucose and D-fructose 6-phosphate, and may be encoded near the gene for fructokinase.

This family is most closely related to the GT1 family of glycosyltransferases. The sucrose-phosphate synthases in this family may be unique to plants and photosynthetic bacteria. This enzyme catalyzes the synthesis of sucrose 6-phosphate from fructose 6-phosphate and uridine 5'-diphosphate-glucose, a key regulatory step of sucrose metabolism. The activity of this enzyme is regulated by phosphorylation and moderated by the concentration of various metabolites and light.

sucrose synthase

sucrose synthase. This model represents sucrose synthase, an enzyme that, despite its name, generally uses rather produces sucrose. Sucrose plus UDP (or ADP) becomes D-fructose plus UDP-glucose (or ADP-glucose), which is then available for cell wall (or starch) biosynthesis. The enzyme is homologous to sucrose phosphate synthase, which catalyzes the penultimate step in sucrose synthesis. Sucrose synthase is found, so far, exclusively in plants and cyanobacteria [Energy metabolism, Biosynthesis and degradation of polysaccharides].

Sucrose synthase. Sucrose synthases catalyze the synthesis of sucrose from UDP-glucose and fructose. This family includes the bulk of the sucrose synthase protein. However the carboxyl terminal region of the sucrose synthases belongs to the glycosyl transferase family pfam00534.