title: Size and shape of the alpha subunit of the (Ca,Mg)-dependent adenosinetriphosphate from Escherichia coli in solution in the presence and absence of ATP.
abstract: The alpha subunit of the (Ca, Mg)-dependent ATPase from Escherichia coli was studied in solution by means of X-ray scattering experiments at variable contrast and in the presence of ATP. The experiments were carried out on an absolute scale in the range of (45.0 nm-1) less than h less than (1.5 nm-1) at pH 8.0. The experiments show that this system and the complex of the alpha subunit with ATP can be considered to be ideal and monodisperse so that the following parameters for the alpha subunit and its complex with ATP were determined: the radius of gyration, the volume, the degree of hydration, the maximum particle diameter, and the molecular weight. The molecular weight of the alpha subunit was determined as 58 500 +/- 3000 by means of light scattering measurements, and 57 700 +/- 25 000 by the small-angle X-ray scattering experiments. The radius of gyration of the alpha subunit at pH 8.0 was determined to 2.64 +/- 0.02 nm, the maximum chord in solution to 10.0 +/- 0.5 nm, the volume to 102.4 +/- 2.5 nm3, and the degree of hydration to 0.34 +/- 0.02 mg X g-1. Binding of ATP to the alpha subunit causes structural changes. These changes are reflected in the radius of gyration, Rg = 2.45 +/- 0.015 nm, in the volume, 117.6 +/- 1.5 nm3, and in the maximum chord length in solution, 7.8 +/- 0.5 nm. These changes imply a decrease of the axial ratio from 2.4 to 1.4, i.e. ATP-binding induced an increase in isometry of the alpha subunit.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D011487:Protein Conformation; D012996:Solutions; D014961:X-Ray Diffraction
chemical_list: D046911:Macromolecular Substances; D012996:Solutions; D000255:Adenosine Triphosphate; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases