Carboxysomal Diffusion Resistance to Ribulose 1,5-Bisphosphate and 3-Phosphoglycerate in the Cyanobacterium Synechococcus PCC7942

Two preparations of ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase(RuBisCO; EC 4.1.2.39[EC]) were obtained from the cyanobacteriumSynechococcus PCC7942. In one preparation, the majority of RuBisCOwas insoluble to be localized in carboxysomes ("CarboxysomalRuBisCOrdquo;), whereas in the other, the enzyme was solubilized("Solubi-lized RuBisCO"). The kinetic properties of both RuBisCOpreparations were determined to elucidate the changes of theactivity based on packing the enzyme in carboxysomes. The activityof Carboxysomal RuBisCO decreased with increasing reaction time.The apparent affinity of the Carboxysomal RuBisCO for RuBP waslower than that of the Solubilized RuBisCO. The 3-phosphoglycerateproduced in carboxysomes was detected with a lag of three minutes.These results suggest that RuBisCO activity changes dependenton packing in carboxysomes and have a diffusion resistance toRuBP and PGA (Received October 31, 1996; Accepted April 11, 1997)