NAD and ADP‐ribose metabolism in mitochondria

Abstract

Mitochondrial metabolism is intimately connected to the universal coenzyme NAD. In addition to its role in redox reactions of energy transduction, NAD serves as substrate in regulatory reactions that lead to its degradation. Importantly, all types of the known NAD-consuming signalling reactions have been reported to take place in mitochondria. These reactions include the generation of second messengers, as well as posttranslational protein modifications such as ADP-ribosylation and protein deacetylation. Therefore, the availability and redox state of NAD emerged as important factors in the regulation of mitochondrial metabolism. Molecular mechanisms and targets of mitochondrial NAD-dependent protein deacetylation and mono-ADP-ribosylation have been established, whereas poly-ADP-ribosylation and NAD-derived messenger generation in the organelles await in-depth characterization. In this review, we highlight the major NAD-dependent reactions occurring within mitochondria and describe their metabolic and regulatory functions. We also discuss the metabolic fates of the NAD-degradation products, nicotinamide and ADPribose, and how the mitochondrial NAD pool is restored.

Fe-S Cluster Biogenesis in Isolated Mammalian Mitochondria

“…1A, compare lanes 7 and 8 with lanes 3 and 6), indicating that the ACO2 signal was not due to covalent incorporation of [ 35 S]cysteine into the polypeptide backbone. This notion is consistent with the observation that the 35 S label associated with ACO2 was completely lost when samples were analyzed by SDS-PAGE (instead of native PAGE) after incubation with [ The radiolabeling of ACO2 was not due to exchange of 35 S into existing clusters of ACO2. For example, when Fe- 35 S clusters were formed and inserted into ACO2, incubation of mitochondria with a large excess of unlabeled cysteine did not remove the radiolabel from ACO2 (Fig.…”

“…The Radiolabeled Endogenous Protein in Mammalian Mitochondria Is Aconitase-We suspected the radiolabeled protein in CAD mitochondria to be aconitase (ACO2) because, in isolated yeast mitochondria, aconitase (Aco1) can be labeled with Fe- 35 S clusters under similar conditions (Fig. 1A, lanes 9 and 10) (15).…”

“…The 35 S labeling of aconitase in our assays does not represent the repair of damaged [3Fe-4S] clusters to functional [4Fe-4S] clusters because this would require incorporation of (unlabeled) iron and not (radiolabeled) sulfur. How then did the protein (ACO2) become radiolabeled?…”

“…The experimental system resembles, in some respects, the system we developed for studying Fe-S cluster synthesis in yeast mitochondria (15)(16)(17). We found that murine CAD 4 mitochondria were able to generate an activated form of sulfur derived from cysteine and bound to the mitochondrial NFS1 cysteine desulfurase (NFS1-S- 35 SH). This activated persulfide sulfur was utilized during the synthesis of new Fe- 35 S clusters and inserted into endogenous apoaconitase or imported apoferredoxins.…”

“…We found that murine CAD 4 mitochondria were able to generate an activated form of sulfur derived from cysteine and bound to the mitochondrial NFS1 cysteine desulfurase (NFS1-S- 35 SH). This activated persulfide sulfur was utilized during the synthesis of new Fe- 35 S clusters and inserted into endogenous apoaconitase or imported apoferredoxins. The overall process was strictly dependent on the availability of GTP, NADH, ATP, and iron.…”