Intermolecular interactions of NADP-malic enzyme and carboxylation phase enzymes in maize leaf extracts

The total protein complex was isolated from the leaves of 3- to 4-week-old maize (Zea mays L.) plants by precipitation with polyethylene glycol (PEG) in the presence of MgCl2. NADP-malic enzyme (ME) and ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activities were revealed, and C-14-bicarbonate was fixed in the presence of D-ribose 5-phosphate (R5P). Subsequent separation of protein fraction components by gel-diffusion and ion-exchange chromatography made it possible to isolate individual proteins, whereas the overlapping zones of peaks displayed the ME activity and the total activity of carboxylation phase enzymes. This carboxylation was manifested by the fixation of (NaHCO3)-C-14 as the acid-resistant substance in the presence of R5P and ATP. Thus, the first evidence of an enzyme association is obtained. In leaf extracts of maize, i.e., a plant with the malic-enzyme type of C-4 photosynthesis, this association consists of ME, ribose 5-phosphate isomerase, phosphoribulokinase, and Rubisco.