NAD(-CELLS BY ELECTROTRANSFECTION LEADS TO INCREASED POLY(ADP-RIBOSYL)ATION CAPACITY() LOADING OF MAMMALIAN)

Many cellular enzymes use NAD(+) as coenzyme or substrate, depending o n the nature of the enzymatic reaction. Under certain conditions the c ellular NAD(+) concentration may become rate-limiting for such enzymes . For instance, when eucaryotic cells are exposed to high concentratio ns of DNA-damaging agents, the resulting DNA strand breaks may stimula te the nuclear enzyme poly(ADP-ribose) polymerase (PARP) to such an ex tent that the cellular pool of NAD(+), which is the substrate for this enzyme, is severely depleted, possibly leading to acute cell death. H ere we show that NAD(+) concentrations in CV-1 monkey and CO60 hamster cells can be raised 3- to 4-fold by electrotransfection of NAD(+). Th is additional NAD(+) is indeed available for PARP to synthesize higher -than-normal amounts of poly(ADP-ribose) after treatment with the alky lating agent N-methyl-N'-nitro-N-nitrosoguanidine. NAD(+) loading of c ells by electrotransfection may be useful also for the study of other cellular reactions in which NAD(+) is involved.