An Application of Isoelectric Focusing in the Purification of Thiamine-binding Protein of Escherichia coli

A partially purified thiamine-binding protein preparation was fractionated by isoelectric fractionation and following results were obtained. 1. The isoelectric fractionation could be used as a method of purification of the binding protein with nearly the same efficiency and recovery as those of conventional purification methods, but it took at least 3-5 days for an expriment. 2. The carrier ampholite covering the pH range of 0.7 (pH 5.5-6.2, 40% concentration) was used in a final concentration of 0.7% with a 440 ml column and was found adequate for the fractionation of 240mg of proteins, which had been liberated from E..coli cells by osmotic shock. 3. The carrier ampholite of the pH range of 0.35 (pH 5.88-6.23) was oreoared and used for the binding protein purification. The final concentration of the ampholite was approx. 0.45% and thiamine-binding activity was recovered in two separate groups of fractions. The recovery in the main activity peak was 51 % with 2.2 times purification in the specific activity and could be used as a purification procedure. 4. The carrier ampholite of narrower pH range(0.35 pH) gave a fractionation product of the specific activity of 8.84 nmole/mg from the sample of 3.96 nmole/mg. The carrier ampholite of 0.7 pH range gave a fractionation product of the specific activity of 1.18 nmole/mg from the sample of 0.61 nmole/mg. Those values indicated that the resolving power of the narrower pH range ampholote was superior to the 0.7 pH range ampholite appreciably.