Studies on actin fragments obtained by digestion with thrombin,BNPS-skatole and nitrothiocyanobenzoic acid

We have isolated fragments of actin prepared by thrombic digestion (residues 40–374 I], and 114–374 II]), BNPS-skatole cleavage (residues 87–339 III]) and nitrothiocyanobenzoic acid treatment (residues 10–216 IV]) using preparative electrophoretic and chromatographic techniques. Analysis of the filament-forming and tropomyosin-binding properties of demonstrably homogeneous fragments revealed that only fragments I and II oculd form F-actin-like filaments after attempted renaturation, and that only fragment I could bind to tropomyosin. These results in addition to our previous studies on actin fragments and chemically-modified intact actin suggest that residues 1–86 and 340–374 are not required for F-actin filament formation, whereas residues 70–86 and/or 340–374 are essential for tropomyosin-binding activity.