Protection of Actin from Heat Denaturation by Various Phallotoxins

Abstract
Phallotoxins protect F-actin [of rabbit skeletal muscle] from heat denaturation at a temperature of 70.degree. C for 3 min. This was shown by difference spectroscopy. G-actin was not protected from heat denaturation by phalloidin. Four toxic phallopeptides showed the same protecting ability; non-toxic seco-compounds had no effect. The non-toxic (S)-phalloidinsulfoxide. A exhibited only a partial protecting activity, corresponding to an affinity for F-actin of about 0.1 of that of the toxic peptides. Evidence for this was obtained from the easy displacement of the sulfoxide A from F-actin by phalloidin and by a spectroscopic dilution titration.

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