STIMULATION OF ENDOGENOUS ADP-RIBOSYLATION BY BREFELDIN-A

Brefeldin A (BFA) is a fungal metabolite that exerts profound and gene rally inhibitory actions on membrane transport. At least some of the B FA effects are due to inhibition of the GDP-GTP exchange on the ADP-ri bosylation factor (ARF) catalyzed by membrane protein(s). ARF activati on is likely to be a key event in the association of non-clathrin coat components, including ARF itself, onto transport organelles. ARF, in addition to participating in membrane transport, is known to function as a cofactor in the enzymatic activity of cholera toxin, a bacterial ADP-ribosyltransferase. In this study we have examined whether BFA, in addition to inhibiting membrane transport, might affect endogenous AD P-ribosylation in eukaryotic cells. Two cytosolic proteins of 38 and 5 0 kDa were enzymatically ADP-ribosylated in the presence of BFA in cel lular extracts. The 38-kDa substrate was tentatively identified as the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase. The BFA-b inding components mediating inhibition of membrane traffic and stimula tion of ADP-ribosylation appear to have the same ligand specificity. T hese data demonstrate the existence of a BFA-sensitive mono(ADP-ribosy l)transferase that may play a role in membrane movements.