THE REGULATION OF RUBISCO BY RUBISCO ACTIVASE

The activity of Rubisco depends on the conversion of the inactive form (E) to the active form (ECM); the binding of the inhibitors CA1P and RuBP to ECM and E, respectively; and the catalytic formation of inhibitory sugar bisphosphates from the enediol intermediate that precedes carboxylation/oxygenation. The regulatory protein, Rubisco activase, modulates the activity of Rubisco by kinetically increasing the dissociation rate of these sugar bisphosphates from their respective enzyme forms in a process that requires ATP hydrolysis. The activity of Rubisco activase is determined by the ATP:ADP ratio, The activity also appears to be influenced by thylakoid membranes in a light-dependent manner, but only a few details of this effect are currently understood, A species dependence in the interaction between heterologous Rubisco and Rubisco activase proteins has been observed, Whether the regulation of Rubisco is a constraint to crop productivity is debatable and will only be decided by detailed study of plants transformed with appropriately modified Rubisco activase and/or Rubisco proteins.