Physicochemical and biochemical properties of squid actin.

Abstract

G-Actin prepared from the obliquely striated mantle muscle of squid by a modified SPUDICH and WATT's method was ultracentrifugally monodisperse with a sedimentation coefficient, S020, w, of 3.3S, and its molecular weight was estimated to be 4.3×104 by SDS disc electrophoresis. The intrinsic viscosity of the squid G-actin was 0.12dl/g, and the viscosity increased by adding 0.1M KCl or 2mM MgCl2 revealing polymerization to F-actin. On ultracentrifugation, the squid F-actin showed 2 faster peaks with sedimentation coefficients corresponding to those of rabbit F-actin. Under the electron microscope, squid F-actin consisted of double stranded filaments, on which a periodicity of 35-36nm was recognized as was also the case with rabbit F-actin. There were no significant differences in amino acid composition among the actins of squid, fish, rabbit and plasmodium. Superprecipitation and viscosity response with added ATP were tested with positive results on the synthetic actomyosin from squid actin and carp myosin. The latter test was compared with one on the natural actomyosin of squid. Squid actin was found similar to the actins of rabbit, fish, and plasmodium actins in the ability to interact with vertebrate myosin. In contraction of the obliquely striated mantle muscle of squid, squid actin appears to be functionally similar to that of vertebrate striated muscle.