Sestini S, Ricci C, Micheli V, Pompucci G
Dipartimento di Biologia Molecolare, Università di Siena, Italy.
Arch Biochem Biophys. 1993 Apr;302(1):206-11. doi: 10.1006/abbi.1993.1200.
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.
烟酰胺单核苷酸腺苷酰转移酶（NMN-AT）活性迄今尚未在人类红细胞中得到证实，因其活性较低。由于它通常位于细胞核中，所以排除了在人类红细胞中发现它的可能性。在此，我们通过高效液相色谱法首次报道了人类红细胞中NMN-AT的证实及特性。该酶依赖Mg2+，对烟酰胺单核苷酸的Km为0.303 mM，对ATP的Km为0.103 mM，Vmax为346 nmol g Hb-1 h-1。粗制品对烟酸单核苷酸也有活性，可产生烟酸腺嘌呤二核苷酸。NMN-AT活性受烟酸单核苷酸抑制，而烟酸腺苷酰转移酶受烟酰胺单核苷酸抑制。通过DEAE-琼脂糖凝胶柱层析实现了NMN-AT的50倍纯化，并测定了其动力学特性。部分纯化的制品保持了其烟酸腺苷酰转移酶活性。根据人类红细胞中NAD代谢的调节对这些发现进行了讨论。
