New insights into the NAD synthesis in mitochondria isolated from fresh and aged-dehydrated tubers of Jerusalem artichoke

Recently, important information on the pathways involved in NAD synthesis in plants is beginning to appear, but many outstanding questions remain. In fact, the mechanism by which nicotinamide nucleotides localize inside the mitochondria is still obscure. Previous work (Di Martino, 2006) has demonstrated that externally added NMN can increase the nicotinamide nucleotide content of mitochondria isolated from both fresh and aged-dehydrated slices of Jerusalem artichoke tubers; thus suggesting both NMN translocation across the mitochondrial membrane and, more interestingly, the existence of mitochondrial NMN-AT activity, which allows for intramitochondrial NAD synthesis from NMN and endogenous ATP. In order to gain some insight into the mechanism by which plant mitochondria can synthesize nicotinamide nucleotides, we reported HPLC experiments that show that plant mitochondria contain a specific NMN adenylyl-tranferase inhibited by PPi and AMP. We determined the kinetic parameters of the enzyme both in fresh and aged-dehydrated slices of Jerusalem artichoke tubers. Dependence of NMN-AT activity on pH and temperature were also investigated. Ref. Di Martino, Pallotta, FISV 2006. PDF created