Phospho adenylylation and phospho ADP-ribosylation, types of covalent protein modification derived from NADP

The structure of NADP implies, in addition to the hydrogen transfer potential, two activated groups: 2'-phospho AMP and 2'-phospho ADP-ribose. Recent findings demonstrate that both can be used to modify covalently eukaryotic proteins. 2'-Phospho adenylylation appears to be an important route of post-translational modification involving various acceptor polypeptides in different subcellular compartments of rat liver. The true substrate of the transferases involved, however, is free 2'-phospho ADP-ribose derived from NADP by the action of NADP glycohydrolase, conferring a new function to the glycohydrolase beyond its purely catabolic action. The second type of modification, 2'-phospho ADP-ribosylation, was detected as an activity of the arginine specific ADP-ribosyl transferase from erythrocytes (Moss and Vaughan, 1978) which in the presence of H1 used NADP in preference to NAD. These findings show that both pyridine nucleotides represent versatile, multifunctional co-factors, serving as hydrogen-transferring as well as group-transferring co-enzymes.