Adenine nucleotides regulate ADP-ribosylation of membrane-bound actin and actin-binding to membranes.

Adenine nucleotides were shown to increase the ADP-ribosylation of actin by Clostridium perfringens iota and Clostridium botulinum C2 toxin in membranes from human platelets, hamster fat cells, rat liver- and rat brain cells. ATP and ATP gamma S were the most effective agents with ATP showing half-maximal and maximal effects at about 2 and 10 microM, respectively. The rank order of various adenine nucleotides were ATP = ATP gamma S > ADP > AMP-PNP >> AMP = cAMP. Guanine nucleotides showed the same rank order of potencies but were less effective than adenine nucleotides. Adenine nucleotides which increased ADP-ribosylation were able to release actin from membranes. [32P]ADP-ribosylated rabbit skeletal muscle actin, which is unable to polymerize, was used as tool to study membrane-binding of actin. The [32P]ADP-ribosylated actin bound to stripped rat liver membranes in a saturable, time- and temperature-dependent manner. ATP inhibited the binding of ADP-ribosylated actin with a half-maximal and maximal inhibitory concentration at about 50 and 300 microM, respectively. The data indicate that actin-binding to membranes is prevented or reversed in the presence of adenine nucleotides thereby increasing the accessibility of actin for ADP-ribosylation by toxins.