Variations in the Specific Activity of Ribulose-1,5-bisphosphate Carboxylase between Species Utilizing Differing Photosynthetic Pathways

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Abstract
The in vitro specific activity of ribulose-1,5-bisphosphate carboxylase (RuBPCase) (micromoles CO2 fixed per minute per milligram enzyme) from a number of C3 and C4 species and one green alga were measured. RuBPCases from species which utilize the C4 pathway have a specific activity ∼2-fold higher than those from C3 species. RuBPCase from Chlamydomonas reinhardtii has a specific activity similar to the C4 enzyme. Higher specific activity forms of RuBPCase are associated with a decreased enzyme affinity for CO2 (increased Km[CO2]). A small but significant difference in the specific activity of RuBPCase from two C4 decarboxylation types was also observed. The relationship between enzymic properties and the presence or absence of a CO2 concentrating mechanism is discussed.