An Assessment of the Rubisco Inhibitor

2-Carboxyarabinitol-1-phosphate, the nocturnal inhibitor of ribulose-1,5-bisphosphate carboxylase/oxygenase is identical with d-hamamelonic acid-2(1)-phosphate. Reasoning is based on theoretical considerations as well as on mass spectra and (1)H- and (13)C-NMR spectra of the phosphate-free compounds. d-Hamamelonic acid-2(1)-phosphate is interpreted as a metabolic derivative of d-hamamelose-2(1),5-bisphosphate which originates in the chloroplast from fructose-1,6-bisphosphate. A simple method for the synthesis of the inhibitor is suggested.