A Rapid Method for Preparing Crystalline b2 Subunit of Tryptophan Synthetase of Escherichia coli in High Yield

A very rapid method for preparing β2 subunit of tryptophan synthetase of Escherichia coli is based on our observation that the apo-β2 subunit is much less soluble in solutions containing ammonium sulfate than is the holo-β2 subunit. This new preparation (Preparation III) and the standard preparation of Wilson and Crawford (Preparation I) have both been crystallized. Two mechanisms are proposed to explain our findings that the β2 subunit crystallizes as the apoenzyme from solutions of ammonium sulfate containing pyridoxal-P and as the holoenzyme from solutions of potassium phosphate containing pyridoxal-P. Crystalline β2 subunit Preparations I and III have high specific activities which are stable when the enzyme is stored in the crystalline form.