Beschreibung:
The α and β2 subunits of tryptophan synthase were investigated by small‐angle X‐ray scattering. The molecular parameters are: radius of gyration, α: 1.95 nm, β2: 3.01 nm; maximum particle diameter, α: 5.8 nm, β2: 10.5 nm; and hydrated volume, α: 60 nm3, β2 160 nm3. The shape of the α subunit can best be described by a circular cylinder, slightly tapered at one end. An elongated elliptical cylinder with its cross section larger in the middle than at the ends was found to be a model equivalent in scattering to the β2 subunit.The α2β2 enzyme complex was found to have a radius of gyration of 4.01 nm, a maximum length of 13.5 nm, and a hydrated volume of 270 nm3. No satisfactory fit of the scattering data was obtainable by mere apposition of the models of the α and β2 subunits. Two cylinders overlapping laterally fit the experimental data considerably better, suggesting changes in the conformation of the subunits on forming the α2β2 complex.