Mitochondria-localized NAD biosynthesis by nicotinamide mononucleotide adenylyltransferase in Jerusalem artichoke (<Emphasis Type="Italic">Helianthus tuberosus</Emphasis> L.) heterotrophic tissues |
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Authors: | Catello Di Martino Maria Luigia Pallotta |
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Institution: | (1) Department of Animal, Plant and Environmental Sciences, University of Molise, Via F. De Sanctis, 86100 Campobasso, Italy;(2) Department of Health Sciences, University of Molise, Via F. De Sanctis, 86100 Campobasso, Italy; |
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Abstract: | Current studies in plants suggest that the content of the coenzyme NAD is variable and potentially important in determining
cell fate. In cases that implicate NAD consumption, re-synthesis must occur to maintain dinucleotide pools. Despite information
on the pathways involved in NAD synthesis in plants, the existence of a mitochondrial nicotinamide mononucleotide adenylyltransferase
(NMNAT) activity which catalyses NAD synthesis from nicotinamide mononucleotide (NMN) and ATP has not been reported. To verify
the latter assumed pathway, experiments with purified and bioenergetically active mitochondria prepared from tubers of Jerusalem
artichoke (Helianthus tuberosus L.) were performed. To determine whether NAD biosynthesis might occur, NMN was added to Jerusalem artichoke mitochondria
(JAM) and NAD biosynthesis was tested by means of HPLC and spectroscopically. Our results indicate that JAM contain a specific
NMNAT inhibited by Na-pyrophosphate, AMP and ADP-ribose. The dependence of NAD synthesis rate on NMN concentration shows saturation
kinetics with K
m and V
max values of 82 ± 1.05 μM and 4.20 ± 0.20 nmol min−1 mg−1 protein, respectively. The enzyme’s pH and temperature dependence were also investigated. Fractionation studies revealed
that mitochondrial NMNAT activity was present in the soluble matrix fraction. The NAD pool needed constant replenishment that
might be modulated by environmental inputs. Thus, the mitochondrion in heterotrophic plant tissues ensures NAD biosynthesis
by NMNAT activity and helps to orchestrate NAD metabolic network in implementing the survival strategy of cells. |
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Keywords: | |
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