CHLOROPLAST INTRAGENIC SUPPRESSION ENHANCES THE LOW CO2/O2 SPECIFICITY OF MUTANT RIBULOSE-BISPHOSPHATE CARBOXYLASE OXYGENASE

  • 25 February 1989
    • journal article
    • research article
    • Vol. 264  (6) , 3051-3053
Abstract
The competition between CO2 and O2 at the active site of ribulose-1,5-bisphosphate carboxylase/oxygenase limits net CO2 fixation in photosynthesis. In the green alga Chlamydomonas reinhardtii a mutation in the chloroplast large-subunit gene reduces the CO2/O2 specificity of the enzyme by 37% and causes valine 331 to be replaced by alanine. Revertant selection identified an intragenic suppressor mutation that increases the CO2/O2 specificity of the mutant enzyme by 33%. This second-site mutation causes threonine-342 to be replaced by isoleucine. The complementing amino acid substitutions flank a catalytically essential lysyl residue at position 334. It thus appears that a number of amino acid residues can influence the CO2/O2 specificity of this bifunctional enzyme. The well defined chloroplast genetics of C. reinhardtii allows the interactions of these residues to be investigated.

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