SIMPLE ENZYME REACTIONS 519 HYDROLYSIS OF GELATIN. Dissolve 6 g. of gelatin in about 250 ml. of warm water. Carry out the formaldehyde titration on 25 ml. of the solution: note in this case that the solu-tion is acid to phenolphthalein. To the remainder of the gelatin solution, add 0-5 to O'8 g. of finely powdered commercial trypsin and incubate at 40°. Carry out the formaldehyde titration on 25 ml. samples at intervals as above. Note that the original solution sets to a gel on standing, but is fluid at 40°, and when removed from the bath usually remains so sufficiently long for a titration to be carried out. It is interesting to observe that, after several hours' digestion, the mixture no longer sets to a gel on standing at room temperature, showing that the gelatin is now replaced by completely water-soluble amino-acids. Urease. The chief sources of this important enzyme are (a) the jack bean (Canavalia enstformis). (ft) the soy (or soja) bean (Glycine hispida). The enzyme is of great value in identifying and estimating urea. The action of urease on urea
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