Transfer reactions glutamine transferase

Neither transfer of single ADPR residues by specific eukaryotic transferases nor the existence of other than ester-type linkages in ADPR protein conjugates were recognized for a number of years [24]. Now, there is increasing evidence that the eukaryotic cell possesses a rather elaborate instrumentarium of ADP-ribosylation reactions to modulate important processes. The use of mono(ADPR) groups for the covalent modification of protein provides a tool that may prove to be as versatile as poly(ADP-ribosyl)ation. In addition to the systems discussed here (alkylated cells, differentiation, tumor promotors), mono(ADP-ribosyl)ation may be involved also in the modulation of protein synthesis [8], in the response to heat shock (M. Jacobson, personal communication), and in glutamine synthesis [25]. Nonenzymic mono(ADP-ribosyl)ation reactions must also be taken into consideration whenever the functions of active (P)ADP-ribose as present in the pyridine nucleotides are studied. Finally, preliminary data may indicate that an additional way to modulate protein functions could be provided by phospho-(ADP-ribosylation) reactions. 

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