The nature of insoluble urease

Soluble urease is prepared by the authors from the jack bean by the use of two principles: (1) repeated precipitation from slightly acid 30 per cent alcohol by cooling and centrifuging; (2) removal of the two globulins, concanavalin A and B, by allowing them to crystallize out from the solution of urease in dilute aqueous neutral phosphate solution. Urease prepared in this manner has an activity of nearly 30,000 units per gram of dry material. A unit is defined by the authors as the amount of urease capable of producing 1 mg. of ammonia nitrogen from a urea phosphate solution in 5 minutes at 20° C.

Contrary to the previous belief of the authors, it is not possible to obtain urease entirely free from carbohydrate by the above mentioned procedure. A large amount of a pentose gum can be washed out during the precipitation by cooling, but small amounts of the gum appear to be firmly bound to some of the protein present. It is possible also that soluble urease is contaminated with traces of the third jack bean globulin, canavalin, although canavalin is insoluble in acid 30 per cent alcohol, the solvent used for extracting urease.

The authors have been able to free urease from the last traces of pentose gum, and also from any canavalin that might be present, by means of a third new principle, the conversion of urease into an insoluble, though still active form. This is effected by adding small amounts of sodium chloride to1 neutral 30 per cent alcohol urease, and allowing the solution to stand in a cool place for one or two days. The alcohol and sodium chloride are not added until after the crystallizable globulins have been removed and the material has been filtered.