ADIABATIC COMPRESSIBILITY OF FLAGELLIN AND FLAGELLAR FILAMENT OF SALMONELLA-TYPHIMURIUM

The partial specific volume and adiabatic compressibility of flagellin , its F40 fragment deprived of the disordered terminal regions, from A la-l to Arg-65 and from Ser-451 to Arg-494, and the flagellar filament of Salmonella typhimurium were determined from the density and the so und velocity measurements at 15 degrees C. The partial specific volume s were 0.728 cm(3)/g, 0.745 cm(3)/g, and 0.734 cm(3)/g, and the partia l specific adiabatic compressibilities were 4.0 X 10(-12) cm(2)/dyn, 6 .7 X 10(-12) cm(2)/dyn, and 4.7 X 10(-12) cm(2)/dyn, for flagellin, F4 0, and the filament, respectively. The smaller values of flagellin tha n those of F40 are reasonably explained by the presence of disordered terminal regions, which are supposed to be highly hydrated by water mo lecules. The volume increase upon polymerization of flagellin into the filament is also confirmed by depolymerization under a high pressure. The smaller volume and compressibility of the filament compared with those of F40 suggest an extensive hydration of the filament on its com plex surface structure, which surpasses the effect on the volume and c ompressibility by a possible increase in the cavity volume at intersub unit interfaces upon polymerization.