Structure and kinetics of plastidic NADP-Malic Enzymes from monocot species

SAIGO, MARIANA; DRINCOVICH, MARÍA FABIANA; ANDREO, CARLOS

Puerto Madryn

Congreso; SAIB. XLVI Reunión Anual; 2010

Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular

The origin of C photosynthesis involved several morphological 4and biochemical adaptations. It is generally assumed that C 4specific enzymes arose by the acquisition of novel regulatoryproperties of duplicated copies of enzymes already present in the C 3ancestors. Maize and sorghum are C grasses in which a 4chloroplastic isoform of NADP-Malic enzyme (NADP-ME)decarboxylates malate to increase the concentration of CO in the 2surroundings of RuBisCO. These monocot plants along with rice, aC monocot, constitute a good model for the study of C evolution. 3 4Besides, maize and sorghum have two plastidic isoforms of NADPME,one involved in photosynthesis which is defined here as C 4type, whereas rice has only one isoform in this organelle. The aim ofthis work was to asses whether the previously reported kinetical andstructural features that distinguish C from non-C isoforms in 4 4maize, can be found in sorghum and rice enzymes. First, theproteins were expressed in E. coli and purified by affinitychromatography. Kinetical parameters such as kcat, K substratesand substrate inhibition were assayed at pH7 and pH8. Additionally,the quaternary structure was determined by non denaturingelectrophoresis. All the data obtained shows that the sequencebasedclassification of NADP-ME isoforms as C or non-C is in 4 4accordance with the kinetical and structural differences herepresented.