| Abstract: | A series of proteins are covalently labeled when human lymphocytes are incubated with 32P]NAD+. The majority of this labeling is effectively inhibited when the lymphocytes are coincubated with 3-aminobenzamide, a potent inhibitor of poly(ADP-ribose) polymerase. However, labeling of a 72 000 molecular weight protein was resistant to the inhibitory effect of 3-aminobenzamide. Labeling of this protein from 32P]NAD+ was shown to be Mg2+-dependent. The 72 000 molecular weight protein could also be labeled on incubation with alpha-32P]ATP, gamma-32P]ATP and 32P]orthophosphate, but not from 3H]NAD+ or 14C]NAD+. In the present study, we show that the 72 000 molecular weight protein is not ADP-ribosylated but rather, phosphorylated on incubation with 32P]NAD+. This phosphorylation appears to occur via an Mg2+-dependent conversion of NAD+ to AMP with the eventual utilization of the alpha-phosphate for phosphorylation of the 72 000 molecular weight protein. |
