Survey of pyruvate, phosphate dikinase activity of plants in relation to the C3, C4 and CAM mechanisms of CO2 assimilation

Abstract The pyruvate, phosphate dikinase activity (PPD, EC 2.7.9.1) associated with crude extracts of leaf tissue of some C 3 and C 4 plants was determined by phosphoenolpyruvate plus PPi-dependent phosphorylation of AMP. The PPD activity of all C 4 plants examined was > 15 nmol/mg protein/min. Several factors contributed to the underestimation of PPD activity in crude extracts of at least some species. Significant PPD activity (> 0.15 nmol/mg protein/min) was not detected in the majority of C 3 species but several C 3 species and the two CAM species studied exhibited activity in the range 0.4–4 nmol/mg protein/min while the C 3 species Avena sativa showed activity up to 8 nmol/mg protein/min. The oat leaf enzyme was partially purified; it exhibited properties similar to those of partially purified PPD from maize. Leaf extracts of the orchids Cymbidium canaliculatum and C. madidum contained high levels of PPD activity similar to the majority of C 4 plants. PPD activity has also been shown in other previously unstudied species.