(RuDP) An outdated term for the initial carbon dioxide acceptor in photosynthesis that has now been replaced by *ribulose bisphosphate
. The terms di- and bis- both refer to the presence of two groups in a molecule. In diphosphates the second phosphate group is added directly to the first (e.g. adenosine diphosphate). In bisphosphates the second phosphate is on a different carbon atom to the first (e.g. ribulose bisphosphate or fructose bisphosphate).