Ribulose-1,5-bisphosphate carboxylase/oxygenase
(Rubisco) is prone to inactivation from non-productive
binding of sugar-phosphates. Reactivation of Rubisco
requires conformational remodeling by a specific chaperone,
Rubisco activase. Rubisco activase from tobacco and other
plants in the family Solanaceae is an inefficient activator of
Rubisco from non-Solanaceae plants and from the green alga
Chlamydomonas reinhardtii. To determine if the Rubisco
small subunit plays a role in the interaction with Rubisco
activase, a hybrid Rubisco (SSNT) composed of tobacco
small subunits and Chlamydomonas large subunits was
constructed. The SSNT hybrid, like other hybrid Rubiscos
containing plant small subunits, supported photoautotrophic
growth in Chlamydomonas, but growth in air was much
slower than for cells containing wild-type Rubisco. The
kinetic properties of the SSNT hybrid Rubisco were similar
to the wild-type enzyme, indicating that the poor growth in
air was probably caused by disruption of pyrenoid formation
and the consequent impairment of the CO2concentrating
mechanism. Recombinant Rubisco activase from Arabidopsis
activated the SSNT hybrid Rubisco and hybrid
Rubiscos containing spinach and Arabidopsis small subunits