Crystalline α2β2 Complexes of Tryptophan Synthetase of Escherichia coli

The native tryptophan synthetase complex of Escherichia coli has been purified and crystallized for the first time. The preparation utilizes a strain of E. coli K-12 which produces both the α and β2 subunits of tryptophan synthetase; about 17% of the total soluble protein of this strain is the tryptophan synthetase complex. A reconstituted tryptophan synthetase complex has also been prepared and crystallized from α and β2 subunits which were separately purified from two different strains of E. coli K-12. Our findings that both the native and reconstituted complexes have the same molecular weight, α2β2 subunit structure, crystalline shape, and specific activities show that the native complex contains no new component and that reconstitution of the complex results in no alteration of the properties of the complex. Tryptophan synthetase can also form a reconstituted αβ2 complex. This complex has been isolated and further characterized.