Structural and functional characterization of human NAD kinase

NADP is essential for biosynthetic pathways, energy, and signal transductio n. Its synthesis is catalyzed by NAD kinase. Very little is known about the structure, function, and regulation of this enzyme from multicellular orga nisms. We identified a human NAD kinase cDNA and the corresponding gene usi ng available database information. A cDNA was amplified from a human fibrob last cDNA library and functionally overexpressed in Escherichia coli. The o btained cDNA, slightly different from that deposited in the database, encod es a protein of 49 kDa. The gene is expressed in most human tissues, but no t in skeletal muscle. Human NAD kinase differs considerably from that of pr okaryotes by subunit molecular mass (49 kDa vs 30-35 kDa). The catalyticall y active homotetramer is highly selective for its substrates, NAD and ATP. It did not phosphorylate the nicotinic acid derivative of NAD (NAAD) sugges ting that the potent calcium-mobilizing pyridine nucleotide NAADP is synthe sized by an alternative route. (C) 2001 Academic Press.