Heteromeric enzymes: Different properties A. thaliana NAD-malic enzyme subunits

TRONCONI, M.; MAURINO, VERÓNICA G; MARIA FABIANA DRINCOVICH; ANDREO, CARLOS S

Mar del Plata, Buenos Aires, Argentina

Congreso; XLIII Reunión anual de la Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular (SAIB); 2007

Sociedad Argentina de Investivaciones en Bioquímica y Biología Molecular

Malic enzyme (ME) is classified into three different types: EC 1.1.1.38, 39 and 40. The class EC 1.1.1.39 is exclusive of plant mitochondria, and it seems to assemble as an heteromeric oligomer. In the present work, the two genes (nad-me1 and 2) encoding A. thaliana mitochondrial ME were studied. The recombinant proteins were separately expressed and characterized. NAD-ME1 and NAD-ME2 showed NAD-ME activity alone, with well-distinct kinetic and regulatory properties. While NAD-ME1 could not be detected by native PAGE revealed by activity, NAD-ME2 showed a dimeric active band. Native PAGE coupled to SDS-PAGE of A. thaliana mitochondrial extracts, indicate that NAD-ME could assemble as a dimer of non-identical subunits in vivo. Further results confirming this conclusion were obtained by reconstitution of the dimer in vitro. The characterization of loss-of function mutants plants for both nad-me genes indicated that each NAD-ME alone exhibits enzymatic activity in vivo, as observed for the recombinant enzymes. In addition, the single and double nad-me mutants showed no visible phenotype under standard conditions. These results indicate that, although A. thaliana NAD-ME assembles as a heterodimer, each subunit can catalyze ME reaction with regulatory and kinetic distinct properties. The results obtained are discussed in terms of the role that this enzyme can fulfill in this C3 plant.