ABSTRACT
Erthrocytes from African blacks with primary hepatoma were incubated with physiological amounts (1.64 microM) of nicotinamide-14C (NM-14C) and it was found that these erythrocytes could synthesize NAD from NM. After 3-hr incubation with NM-14C, a large percentage of the 14C was found in NMN, nicotinamide riboside (NR) and NAD, but was undetectable in nicotinic acid nucleotides (NAMN and NAAD). This suggested that the NAD synthesized from NM was not through the Preiss-Handler pathway. After 6-plus hr incubation, the 14C found in NAMN and NAAD suggested the NAD synthesized was being broken down and reutilized through Preiss-Handler pathway for synthesis of NAD. This reutilization pathway was confirmed by incubating nicotinic acid-14C (NA-14C) with erythrocytes. Apparently the metabolites from the breakdown of NAD were deaminated. The metabolism of NM-14C was slower than NA-14C. However, after 24 hr incubation with NM-14C, 72.26% of 14C was found in NAD. A high percentage of 14C in NR at the initial incubation and a later drop suggested that NR was another intermediate in the pathway.
