Uptake of nicotinamide adenine dinucleotide and excretion of its degradation pro­ducts by tissue culture cells

For the purpose to reveal the mechanism of uptake and degradation of NAD by cells, the authors conducted the observation on the L cells cultured in the medium containing NAD and the following results have been obtained. 1. NAD in the medium is taken up by the cells in its intact form, reaching about twice the value of the control. 2. The spontaneously degraded products of NAD, nicotinamide and adenine dinucleotide ribose, in the same molar concentration as NAD used in the present experiment, have no effect on the NAD content of L cells. 3. The NAD taken up by the cells is degraded into nicotinamide mononucleotide (NMN) and adenine mononucleotide (AMP) by pyrophosphatase including NADpptase and excreted in the medium. Unexpectedly the ingested NAD is not degraded by NADase in the L cell. 4. L cells metabolize the same amount of NAD as that contained originally in the cell for about ten minutes, as calculated from the amount of NMN excreted in the medium.