Catalysis of ribulosebisphosphate carboxylase/oxygenase activation by the product of a Rubisco activase cDNA clone expressed in Escherichia coli

Ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) activase activity was obtained from a partially purified extract of Escherichia coli transformed with a 1.6-kilobase spinach (Spinacia oleracea L.) cDNA clone. This activity was ATP-dependent. Catalysis of rubisco activation by spinach and cloned rubisco activase was accompanied by the same extent of carboxyarabinitol bisphosphate-trapped 14CO2 as occurred in spontaneous activation, indicating that rubisco carbamylation is one facet of the rubisco activase reaction. The CO2 concentration required for one-half maximal rubisco activase activity was about 8 micromolar CO2. These observations are consistent with the postulated role of rubisco activase in regulating rubisco activity in vivo.