Specifically, this enzyme catalyzes the transfer of a hexosyl group from uridine diphosphate glucose (UDP-glucose) to D-fructose 6-phosphate to form UDP and D-sucrose-6-phosphate.

[1] In the open conformation of H. orenii SPS, fructose 6-phosphate forms hydrogen bonds with Gly-33 and Gln-35 residues in the A domain while UDP-glucose interacts with the B-domain.

In this closed conformation, the Gly-34 residue of the A domain interacts with UDP-glucose and forces the substrate to adapt a folded structure, facilitating its donation of the hexosyl group.

[4] After binding, fructose 6-phosphate will interact with UDP via a hydrogen bond, which lowers the activation energy of the reaction and stabilizes the transition state.

[3] This regulation strategy also controls carbon flux from photosynthesis, as studies indicate the signal transduction pathway responsible for SPS activation responds to light stimulus.

[5][6][7] Glucose 6-phosphate binds to an allosteric site, resulting in conformational changes to SPS that increase the enzyme's affinity for the glucosyl accepting substrate.

SPS plays a major role in partitioning carbon between sucrose and starch in photosynthetic and non-photosynthetic tissues, affecting the growth and development of the plant.