Clostridium perfringens iota toxin ADP-ribosylates actin. Substrates of C. perfringens toxin are both non-muscle β/γ-actin and skeletal muscle actin. This finding suggests that C. perfringens iota ADP-ribosylates the same amino acid in skeletal muscle and non-muscle actin as does C. botulinum C2 toxin in non-muscle actin. Protein chemical analysis involving thermolysin cleavage on [32P]ADP-ribosylated actin or tryptic digestion followed by a secondary thermolysin cleavage of the radiolabelled fragments showed one major site of ADP-ribosylation. From its amino acid composition and sequence, the radiolabelled peptide was identified as peptide 175–177, locating the acceptor ADP-ribosyl amino acid as Arg-177.
