Carboxylterminal deletion mutants of ribulosebisphosphate carboxylase from Rhodospirillum rubrum.

The carboxylterminal octapeptide of ribulosebisphosphate carboxylase from Rhodospirillum rubrum, which lacks small subunits, shows homology to a highly conserved region near the amino terminus of the small subunits of hexadecameric ribulosebisphosphate carboxylases, which are composed of large and small subunits. Truncations of the R. rubrum enzyme, which partially or completely deleted the region of homology, demonstrated that the region is not an important determinant of the catalytic efficiency of the enzyme. A further truncation, which replaced the carboxylterminal 19 amino acid residues with a single terminal leucyl residue, yielded a Rubisco whose substrate-saturated catalytic rate resembled that of the wild-type enzyme but which had weaker affinities for ribulose-P2 and CO2.