NAD synthases 1 and 2 (NADSYN1 and NADSYN2) catalyse the final step in the biosynthesis of NAD+, both in de novo synthesis and in the salvage pathway. The enzymes makes use of an amide donor in the reaction. NADSYNs exist as a homohexamers in the cytosol. The major difference between the two forms is that NADSYN1 appears to be glutamine-dependent whereas NADSYN2 is strictly ammonia-dependent (Hara et al. 2003).