Diurnal Changes of Fructose-6-phosphate,2-kinase and Fructose-2,6-bis-phosphatase Activities in Spinach Leaves

Extracts have been rapidly prepared from spinach leaves, and the activity of fructose-6-phosphate, 2-kinase (Fru6P,2kinase) and fructose-2,6-bisphosphatase (Fru2.6P2ase) measured. The enzyme activities do not change during light-dark transitions, but there is an increase of Fru6P,2- kinase and decrease of Fru2,6P2ase activity over several hours in the light. This increase of the Fru6P,2kinase: Fru2,6P2:ase ratio shows that a previously unrecognized mechanism, which may include protein modification, controls Fru2,6P2 levels in leaves. It operates as sucrose accumulates in the leaf, and will be involved in regulating the partitioning of photosynthate.