Nanosecond fluorometric investigation of hydrodynamic properties of adenosine triphosphatase from thermophilic bacterium PS3

The soluble portion (TF₁) of proton-translocating ATPase from thermophilic bacterium PS3 was labeled with a fluorescent dye N-(1-pyrene)maleimide. The decay of fluorescence anisotropy of the adduct showed that TF₁ in aqueous solution was characterized by a volume of equivalent sphere of 1, 120 nm³. This value is 2.4 times the volume calculated from the molecular weight and partial specific volume, indicating a non-spherical shape and/or extensive hydration. A prolate ellipsoid with an axial ratio of 2 to 3 is suggested as a first approximation of the shape of hydrated TF₁. The presence or absence of ATP, ADP, or Mg²⁺ did not alter the volume of the equivalent sphere appreciably; the probable conformational change of TF₁ induced by these ligands does not lead to a gross alteration of its hydrody-namic properties.