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 gly col (PEG) in the presence of MgCl2. NADP-malic enzyme (ME) and ribulos e 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activities were rev ealed, and C-14-bicarbonate was fixed in the presence of D-ribose 5-ph osphate (R5P). Subsequent separation of protein fraction components by gel-diffusion and ion-exchange chromatography made it possible to iso late individual proteins, whereas the overlapping zones of peaks displ ayed the ME activity and the total activity of carboxylation phase enz ymes. This carboxylation was manifested by the fixation of (NaHCO3)-C- 14 as the acid-resistant substance in the presence of R5P and ATP. Thu s, the first evidence of an enzyme association is obtained. In leaf ex tracts of maize, i.e., a plant with the malic-enzyme type of C-4 photo synthesis, this association consists of ME, ribose 5-phosphate isomera se, phosphoribulokinase, and Rubisco.