NAD BIOSYNTHESIS IN HUMAN PLACENTA: CHARACTERIZATION OF HOMOGENEOUS NMN ADENYLYLTRANSFERASE

The nuclear location of NMN adenylyltransferase (NMNAT), the last enzyme in the main biosynthetic pathway of NAD+, prompted us to investigate about a possible involvement of this enzyme in the regulation of the cellular activity by hypothesizing its eventual relationship with poly(ADP-ribose) polymerase (ADPRP), another chromatin bound enzyme. This hypothesis was based on the discovery of an inhibitory effect exerted by NMNAT on ADPRP in vitro in reconstituted systems, composed by enzymes purified both from different sources (heterologous system) (1) and from identical sources (homologous system) (2). In order to verify such a phenomenon in man and to better elucidate its functional significance we carried out the purification of NMNAT from human placenta, where the system involved in NAD+ comsumption has been fully characterized (3).