Alkaline C-1 Fructose-1,6-diphosphatase : Evidence for its Participation in Photosynthesis

PATHWAYS proposed for the conversion of carbon dioxide to hexose monophosphate during photosynthesis require the cleavage of the phosphate linked to carbon-1 of either fructose-1,6-diphosphate, or sedoheptulose-1,7-diphosphate, or both1–3. A C-1 alkaline phosphatase specific for fructose-1,6-diphosphate has been prepared from spinach leaves and characterized by Racker and Schroeder3. This enzyme was not thought to participate in photosynthesis since it did not appear to be localized in the chloroplasts. Recently it was reported4 that pea chloroplasts isolated in various aqueous media lost about 90 per cent of their ribulose-1,5-diphosphate carboxylase, an enzyme considered to play an essential part in photosynthesis1. Since this finding indicated that photosynthetic enzymes were not necessarily retained in chloroplasts isolated by the usual procedures, the possible function and intracellular distribution of alkaline fructose-1,6-diphosphatase in photosynthetic tissues were re-investigated.