Study of the pyruvate carboxylase activity of NADP-malic enzyme in C3 plants

BADIA, M. B.; ARIAS, C. L.; ANDREO, C. S.; DRINCOVICH, M. F.; GERRARD WHEELER, M. C.

Mar del Plata

Congreso; LI Reunión Anual SAIB; 2015

SAIB

NADP-malic enzyme (NADP-ME) catalyzesthe reversible oxidative decarboxylation of malate to pyruvate, CO2and NADPH. In A.thaliana, cytosolicNADP-ME2 is the isoform that mostly contributes to the forward NADP-MEactivity. Studies with recombinant NADP-ME2 showed that it also has a highcatalytic efficiency for the reverse reaction, i.e., the reductive carboxylation of pyruvate, and that thisactivity is differentially regulated by cell metabolites and pH. In this work, Arabidopsis mutant and overexpressinglines in NADP-ME2 were used to assess this possible anaplerotic reaction of NADP-ME.Total pyruvate carboxylation activitywas measured in leaf extracts, being lower in plantslacking NADP-ME2 and higher in overexpressing lines, compared to wild type. Inaddition, the level of substrates and products of the reaction was analyzed.The plants overexpressing NADP-ME2 displayed higher malate and lower pyruvatecontent relative to wild type throughout day and night.Moreover, NADP/NADPH ratio was increased in these plants during the night. Theseresults suggest that NADP-ME2 may be preferentially catalyzing the reverse overthe forward reaction in the overexpressing lines. Thus, the pyruvate carboxylase activity of NADP-ME may take place inplant cells, contributing to the synthesis of C4 compounds and beingregulated by cell metabolic status and environmental changes.