The Inactivation of Crystallized Urease by Water and Its Prevention.

Abstract

Crystallized urease 1 , 2 diluted with 100,000 times its weight of water, so that each cubic centimeter contains approximately one unit, is very rapidly inactivated at room temperature. The curve obtained when time is plotted against activity is practically a rectangular hyperbola. This inactivation by water is prevented more or less completely by amino acids, proteins, buffered cyanide, phosphates, and by many colloids other than proteins. Some of these colloids are: gum arabic, boiled starch, glycogen, aluminum hydroxide gel, gum mastic suspension and castor oil suspension. Glycocoll and alanin in 1 per cent solution do not afford complete protection, but neutral 2 per cent gum arabic protects perfectly. On account of this fact, 2 per cent gum arabic can be used to dilute crystallized urease when it is necessary to do so in order to test its activity. The protective action of phosphates is greater at pH 6.1 than at neutrality. Urease that has been largely inactivated 1 by water can be partly reactivated by adding either gum arabic or amino acids. Urease is doubtless protected by urea, and also appears to protect itself. Urease crystals dissolved in only 1300 times their weight of water lose no more than 2 or 3 per cent of their activity during the first hour, as compared with a urease solution made by diluting the same quantity of crystals to the same volume, with 2 per cent gum arabic solution.

Impure urease solutions are largely protected by their impurities and show no measurable protective action by added amino acids and colloids when one unit of enzyme per cc. is tested for a period of 5 minutes.