INVESTIGADORES
TRONCONI Marcos Ariel
artículos
Título:
NAD-malic enzymes of Arabidopsis thaliana display distinct kinetic mechanisms that support differences in physiological control
Autor/es:
MARCOS A. TRONCONI, MARIEL C. GERRARD WHEELER, VERÓNICA G. MAURINO, MARÍA F. DRINCOVICH AND CARLOS S. ANDREO
Revista:
BIOCHEMICAL JOURNAL
Editorial:
PORTLAND PRESS LTD
Referencias:
Año: 2010 vol. 430 p. 295 - 303
ISSN:
0264-6021
Resumen:
The Arabidopsis thaliana genome contains two genes encoding NAD-MEs [NAD-dependent malic enzymes; NAD-ME1 (TAIR accession number At4G13560) and NAD-ME2
(TAIR accession number At4G00570)]. The encoded proteins are localized
to mitochondria and assemble as homo- and hetero- dimers in vitro and in vivo.
In the present work, the kinetic mechanisms of NAD-ME1 and -ME2
homodimers and NAD-MEH (NAD-ME heterodimer) were studied as an approach
to understand the contribution of these enzymes to plant physiology.
Product-inhibition and substrate-analogue analyses indicated that
NAD-ME2 follows a sequential ordered Bi-Ter mechanism, NAD being the
leading substrate followed by L-malate. On the other
hand, NAD-ME1 and NAD-MEH can bind both substrates randomly. However,
NAD-ME1 shows a preferred route that involves the addition of NAD first.
As a consequence of the kinetic mechanism, NAD-ME1 showed a partial
inhibition by L-malate at low NAD concentrations. The
analysis of a protein chimaeric for NAD-ME1 and -ME2 indicated that the
first 176 amino acids are associated with the differences observed in
the kinetic mechanisms of the enzymes. Furthermore, NAD-ME1, -ME2 and
-MEH catalyse the reverse reaction (pyruvate reductive carboxylation)
with very low catalytic activity, supporting the notion that these
isoforms act only in L-malate oxidation in plant
mitochondria. The different kinetic mechanism of each NAD-ME entity
suggests that, for a metabolic condition in which the mitochondrial NAD
level is low and the L-malate level is high, the activity of NAD-ME2 and/or -MEH would be preferred over that of NAD-ME1.