This family of archaeal proteins exhibits nicotinamide-nucleotide adenylyltransferase (NMNAT) activity utilizing the salvage pathway to synthesize NAD. In some cases, the enzyme was tested and found also to have the activity of nicotinate-nucleotide adenylyltransferase an enzyme of NAD de novo biosynthesis, although with a higher Km. In some archaeal species, a number of proteins which are uncharacterized with respect to activity, are also present.