One-step affinity purification of Bacillus neutral proteases using bacitracin-silica

A purification procedure for neutral proteases from bacilli is described, in which bacitracin-silica was used as affinity medium. This enabled a one-step purification of the proteases directly from culture supernatant. Since neutral proteases are extremely sensitive towards autodigestion, conditions were chosen such, that autodigestion was largely prevented. Isopropanol appeared to be useful in both eluting the enzymes from the affinity medium, and inhibiting enzymatic activity during this step. The bacitracin-silica medium allowed high flow rates: with columns prepared for use in an FPLC system flow rates up to one column volume per minute were feasible, and still gave satisfactory results. The neutral proteases purified by this method were found to be homogeneous both by SDS-PAGE and analytical gel filtration.