Mutations in a sequence near the N-terminus of the small subunit alter the CO2/O2 specificity factor for ribulose bisphosphate carboxylase/oxygenase

Seven unique substitutions have been introduced by site-directed mutagenesis into the first conserved region of the small subunit of ribulose bisphosphate carboxylase/oxygenase from Anacystis nidulans 6301. After expression of each large, altered-small subunit gene tandem in Escherichia coli, two substitutions in the small subunit tyr17-->asp17 (Y17D) and arg10-->gly10(R10G) result in little or no carboxylase activity. For the latter substitution, no L8S8 enzyme complex could be detected suggesting that this mutation prevents assembly. Mutant enzymes containing the following substitutions R11G, T14A, S16A, Y17D and P19A have CO2/O-2 specificity factors (tau values) of 40, 35, 18, 39 and 44, respectively, compared with that of 44 for wild-type recombinant enzyme whereas P20A has full carboxylase activity and a tau value of 55.