3-hexulose-6-phosphate synthase (, <small>D</small>-arabino-3-hexulose 6-phosphate formaldehyde-lyase, 3-hexulosephosphate synthase, 3-hexulose phosphate synthase, HPS) is an enzyme with systematic name <small>D</small>-arabino-hex-3-ulose-6-phosphate formaldehyde-lyase (<small>D</small>-ribulose-5-phosphate-forming). This enzyme catalyses the following chemical reaction
This enzyme requires Mg<sup>2+</sup> or Mn<sup>2+</sup> for maximal activity.