Nucleoside salvage pathway for NAD biosynthesis in Salmonella typhimurium

Abstract
A previously undescribed nucleoside salvage pathway for NAD biosynthesis is defined in S. typhimurium. Since neither nicotinamide nor nicotinic acid is an intermediate in this pathway, this 2nd pyridine nucleotide salvage pathway is distinct from the classical Preiss-Handler pathway. The evidence indicates that the pathway is from nicotinamide ribonucleoside to NMN and then to nicotinic acid mononucleotide, followed by nicotinic acid adenine dinucleotide and NAD. The utilization of exogenous NMN for NAD biosynthesis was reexamined and in vivo evidence is provided that the intact NMN molecule traverses the membrane.