Nicotinamide mononucleotide adenylyltransferase activity in human erythrocytes

Nicotinamide mononucleotide adenylyltransferase (NMN-AT) activity has not hitherto been demonstrated in human red blood cells, owing to its low activity. Since it is usually located in the nucleus, the possibility of finding it in human erythrocytes was excluded. Here we report the first demonstration and characterization of NMN-AT in human red blood cells, by an HPLC method. The enzyme is Mg2+ dependent, with a Km of 0.303 mM for nicotinamide mononucleotide and 0.103 mM for ATP, and a Vmax of 346 nmol g Hb-1 h-1. The crude preparation is also active on nicotinic acid mononucleotide, producing nicotinic acid adenine dinucleotide. NMN-AT activity is inhibited by nicotinic acid mononucleotide, and nicotinic acid adenylyltransferase is inhibited by nicotinamide mononucleotide. Fiftyfold purification of NMN-AT was achieved by DEAE-Toyopearl chromatography, and the kinetic characteristics were determined. The partially purified preparation maintained its nicotinic acid adenylyltransferase activity. These findings are discussed in light of the regulation of NAD metabolism in human red blood cells.