Maize recombinant non-C4 NADP-malic enzyme: a novel dimeric enzyme with high specific activity

MARIANA SAIGO; FEDERICO BOLOGNA; CARLOS ANDREO; MARÍA F. DRINCOVICH

Bariloche, Argentina

Congreso; Sociedad Argentina de Investigación en Bioquímica y Biología Molecular XXXIX Reunión Anual; 2003

ociedad Argentina de Investigación en Bioquímica y Biología Molecular

In plants, different isoforms of the NADP-malic enzyme (NADP-ME) are involved in a wide range of metabolic pathways, being the most abundant the C4-specific enzyme, which has evolved from C3-type malic enzymes. In maize, the most recent ancestor of C4 NADP-ME is a plastidic non-photosynthetic NADP-ME, whose cDNA has been recently isolated and supposed to codify for a 72 kDa NADP-ME. In the present work, we express a cDNA encoding for this maize non-photosynthetic NADP-ME in E. coli. However, in contrast to the enzyme previously purified from etiolated leaves and roots, the recombinant NADP-ME thus obtained presents different molecular mass (66 kDa per monomer) and kinetic and structural properties, presenting very high intrinsic NADP-ME activity, which is unexpected for a non-C4 NADP-ME. Using antibodies against this recombinant enzyme, an immunoreactive band of 66 kDa is detected in different maize tissues, which expression pattern correlates with that of the 72 kDa protein, indicating that the 66 kDa enzyme is in fact an in vivo expressed protein. The recombinant NADP-ME assembles as a dimer in vitro, although the results obtained suggest that the tetramer found in maize roots in vivo is made up by this 66 kDa NADP-ME, probably in association to the 72 kDa protein. In this way, in the present work we characterize a novel maize NADP-ME not identified until now. This contribution will be of great importance for further studies concerning the equilibrium between the oligomeric states of the NADP-ME isoforms and the evolution towards the C4 isoenzyme in maize.