CEFOBI   05405
CENTRO DE ESTUDIOS FOTOSINTETICOS Y BIOQUIMICOS
Unidad Ejecutora - UE
artículos
Título:
Fumarate and cytosolic pH as modulators of the synthesis or consumption of C4 organic acids through NADP-malic enzyme in Arabidopsis thaliana
Autor/es:
ARIAS, C. L.; ANDREO, C. S.; DRINCOVICH, M. F.; GERRARD WHEELER, M. C.
Revista:
PLANT MOLECULAR BIOLOGY
Editorial:
SPRINGER
Referencias:
Lugar: Berlin; Año: 2012 vol. 81 p. 297 - 307
ISSN:
0167-4412
Resumen:
Arabidopsis thaliana is a plant species that accumulates high levels of organicacids and uses them as carbon, energy and reducing power sources. Among the enzymesthat metabolize these compounds, one of the most important ones is malic enzyme(ME). A. thaliana contains four malic enzymes (NADP-ME 1-4) to catalyze thereversible oxidative decarboxylation of malate in the presence of NADP. NADP-ME2 isthe only one located in the cell cytosol of all Arabidopsis organs providing most of thetotal NADP-ME activity. In the present work, the regulation of this key enzyme byfumarate was investigated by kinetic assays, structural analysis and a site-directedmutagenesis approach. The final effect of this metabolite on NADP-ME2 forwardactivity not only depends on fumarate and substrate concentrations but also on the pH ofthe reaction medium. Fumarate produced an increase in NADP-ME2 activity by bindingto an allosteric site. However at higher concentrations, fumarate caused a competitiveinhibition, excluding the substrate malate from binding to the active site. Thecharacterization of ME2-R115A mutant, which is not activated by fumarate, confirmsthis hypothesis. In addition, the reverse reaction (reductive carboxylation of pyruvate) isalso modulated by fumarate, but in a different way. The results indicate pH-dependenceof the fumarate modulation with opposite behavior on the two activities analyzed.Thereby, the coordinated action of fumarate over the direct and reverse reactions wouldallow a precise and specific modulation of the metabolic flux through this enzyme,leading to the synthesis or degradation of C4 compounds under certain conditions. Thus,the physiological context might be exerting an accurate control of ME activity in planta,through changes in metabolite and substrate concentrations and cytosolic pH.