Small-angle X-ray scattering studies of Escherichia colil-asparaginase

Small angle X-ray scattering studies on Escherichia colil-asparaginase solutions show that the enzyme has a radius of gyration of 34.0 Å ± 0.5 Å at pH 7. The radius of gyration of the dissociated monomer is 16.0 Å ± 1.0 Å; it has the general shape of a prolate ellipsoid with an axial ratio of 1.4. A tetramer of four such ellipsoids arranged with 222 symmetry gives good agreement between measured and calculated radii of gyration if the distance between subunit centers is 43 Å. The tetramer dissociates on dilution below 1% and at pH values below 3.0. Acid-induced denaturation at pH 2.0 is irreversible in contrast to the reversible guanidine-HCl-induced denaturation.