title: Partial specific volume and adiabatic compressibility of G-actin depend on the bound nucleotide.
abstract: We determined the partial specific volume and partial specific adiabatic compressibility of either ATP- or ADP-bound monomeric actin in the presence of Ca(2+) by measuring the density of and sound velocity in a monomeric actin solution at 18 degrees C. The partial specific volume of ATP-bound monomeric actin, equal to 0.744 cm(3)/g, which is exceptionally high among globular proteins, was reduced to 0.727 cm(3)/g when the tightly bound ATP was replaced with ADP. Associated with this, the adiabatic compressibility of ATP-bound monomeric actin, equal to 8.8 x 10(-12) cm(2)/dyne, decreased to 5.8 x 10(-12) cm(2)/dyne, which is a common value for globular proteins. These results suggested that an extraordinarily soft global conformation of ATP-bound monomeric actin is packed into a compact mass associated with the hydrolysis of bound ATP. When monomeric actin was limitedly proteolyzed at subdomain 2 with subtilisin, the nucleotide-dependent flexibility of the global conformation of monomeric actin was lost.
authors.affiliation: Department of Physics, Faculty of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan. kikumoto@crl.go.jp
authors.forename: Mahito
authors.initials: M
authors.lastname: Kikumoto
authors.forename: Youjiro
authors.initials: Y
authors.lastname: Tamura
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ooi
authors.forename: Koshin
authors.initials: K
authors.lastname: Mihashi
mesh_terms: D000199:Actins / Q000737:chemistry* / Q000378:metabolism; D000244:Adenosine Diphosphate / Q000737:chemistry* / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D018482:Muscle, Skeletal / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D011817:Rabbits; D020860:Subtilisin / Q000378:metabolism; D013816:Thermodynamics
chemical_list: D000199:Actins; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D020860:Subtilisin