The effect of phalloidin on filaments polymerized from ADP-actin monomers of the heart muscle was investigated with differential
scanning calorimetry. Heart muscle contains α-skeletal and α-cardiac actin isoforms. In the absence of phalloidin the melting
temperature was 55°C for the α-cardiac actin isoform and 58°C for the α-skeletal one when the filaments were generated from
ADP-actin monomers. After the binding of phalloidin the melting temperature was isoform independent (85.5°C). We concluded
that phalloidin stabilized the actin filaments of α-skeletal and α-cardiac actin isoforms to the same extent when they were
polymerized from ADP-actin monomers.