||P.406 right column 2nd paragraph: "Evidence for Similar Function of α- and β-Carboxysomes: Rubisco Content-The two strains examined in this study had Rubisco active site densities, which were measured on a Chl [Chlorophyll] basis (6 to 14 nmol/mg Chl, Table I), similar to those densities measured previously in Synechococcus spp. at high and low CO2 (Emlyn-Jones et al., 2006 Tables I, III, and IV). Nonetheless, Rubisco active site density increased in both strains in response to low CO2 (Table I), doubling in Synechococcus spp. and increasing approximately 1.5-fold in Cyanobium spp. However, Rubisco active site concentration (expressed on a cellular basis mol/cell) increased approximately 1.5-fold in Synechococcus spp. but remained relatively constant in Cyanobium spp. in response to low CO2. These apparent differences were because of changes in Chl content per cell and cell volume in response to growth under low CO2 (Table I). These changes in cell volume in response to CO2 resulted in similar Rubisco active site concentrations expressed on a cell volume basis (millimolar) in both strains, and an approximate doubling of these values under low-CO2 growth (Table I)."