sucrosephosphate

Sucrose phosphate, commonly known as sucrose-6-phosphate, is the phosphorylated ester of sucrose that serves as a transient intermediate in the biosynthesis of sucrose in plants. The phosphate group is attached to the sixth carbon of the glucose moiety, yielding a phosphorylated sugar link before final conversion to sucrose.

Biosynthesis and function: Sucrose-6-phosphate is formed by the enzyme sucrose-phosphate synthase (SPS) through the condensation of UDP-glucose and fructose-6-phosphate. This reaction produces sucrose-6-phosphate and UDP as a byproduct. The phosphate group is then removed by sucrose-phosphate phosphatase (SPP) to yield free sucrose. This two-step process sits at a key regulatory point in carbon partitioning, influencing how fixed carbon is directed toward sucrose synthesis and translocation in the plant. SPS and SPP activities are subject to regulation by developmental cues, light, and the plant’s sugar status, helping coordinate photosynthate production with growth and metabolism.

Occurrence and significance: Sucrose-6-phosphate is found in higher plants and some algae as part of the normal sucrose biosynthetic pathway. It is not a storage compound itself but a short-lived intermediate whose levels reflect the flux through SPS and the plant’s regulatory state. Because sucrose is a major transport sugar in many plants, the regulation of this intermediate influences carbon allocation to growth, phloem loading, and stress responses.

Chemical properties: As a phosphorylated disaccharide, sucrose-6-phosphate is highly polar and water-soluble. It is typically present at low concentrations and rapidly converted to sucrose in vivo.