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THE ROYAL SOCIETY OF CANADA 



require to be rather carefully defined. We were led, therefore, to 

 study the effect of various factors upon the arginase reaction, and 

 have examined in the first place the influence of hydrogen ion con- 

 centration and of temperature. 



Hydrogen Ion Concentration. A series of mixtures was made, 

 each of which contained 5 c.c. of an arginine solution (capable of 

 yielding 3 mgm. of urea nitrogen), 5 c.c. of a suitabl - buffer mixture 

 (series of Clark and Lubs) and 2 c.c. of arginase extract; after one 

 hour at 21°C the action of the arginase was stopped by a jet of live 

 steam, the mixtures were neutralized, and the urea in each determined. 

 The results are shown in Table I. 



TABLE I 



They show a very sharply defined optimum at Ph = 7.0. The 

 depressing effect of an excess of hydrogen ions is especially conspicuous. 

 In media of increasing alkalinity the speed of the reaction sinks rather 

 less rapidly; an experiment not included in the table showed that 

 even at Ph = 8.8 (but in the absence of a buffer) 20% of the arginine 

 was decomposed in one hour. 



Temperature. Ten c.c. of arginine solution (capable of yielding 

 10.86 mgm. of nitrogen as urea) were treated with 4 c.c. of arginase 

 extract, and 5 c.c. of a neutral phosphate buffer solution. The 

 mixture, diluted to 50 c.c, was maintained for one hour in a thermostat 

 at a specified temperature, and the urea determined in the usual way 

 after the activity of the arginase had been destroyed by heat. The 

 results of a series of such experiments appear in Table II. 



