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

The in vitro specific activity of ribulose-1,5-bisphosphate carboxylase (RuBPCase) (micromoles CO(2) fixed per minute per milligram enzyme) from a number of C(3) and C(4) species and one green alga were measured. RuBPCases from species which utilize the C(4) pathway have a specific activity approximately 2-fold higher than those from C(3) species. RuBPCase from Chlamydomonas reinhardtii has a specific activity similar to the C(4) enzyme. Higher specific activity forms of RuBPCase are associated with a decreased enzyme affinity for CO(2) (increased K(m)[CO(2)]). A small but significant difference in the specific activity of RuBPCase from two C(4) decarboxylation types was also observed. The relationship between enzymic properties and the presence or absence of a CO(2) concentrating mechanism is discussed.