New York Agricultural Experiment Station. 303 



NH4OH, the calcium phosphate having been removed as completely 

 as practicable. 



(3) Treatment as in (2) but prolonged. Preparation B (20 

 grams) was treated as in the preceding experiment, except that 

 the mixture was allowed to stand seventy-two hours (instead of 

 twelve) at 37° C. The amount of casein recovered was 12.4 grams 

 containing 0.721 per ct. of phosphorus. The prolonged treatment, 

 giving opportunity for increased hydrolysis of casein, did not change 

 the percentage of phosphorus in the casein recovered. 



III. THE ACTION OF RENNIN ON CASEIN. 



(Second paper.) 

 ALFRED W. BOSWORTH. 



INTRODUCTION. 



In order to determine if the change from casein to paracasein 

 results in the cleavage of any of the elements contained in the casein 

 molecule it is imperative that pure casein" be used as a standard 

 of comparison, and that the rennin activity be positively differ- 

 entiated from any further proteolytic activity of the enzyme under 

 consideration, for it is quite evident that " Rennin action is prob- 

 ably a hydrolytic cleavage and may be considered the first step 

 in the proteolysis of casein. It would follow from this that the 

 action now attributed to rennin may be produced by any proteolytic 

 enzyme." 8 



experimental. 



Pure casein and paracasein were prepared according to the methods 

 previously published. 9 Pure paracasein was also prepared by 

 allowing trypsin to act upon fat-free milk after the addition of 

 calcium chloride, and the curd produced was purified according to 

 the method referred to. The use of an excess of ammonia as pre- 

 scribed has been criticised by Harden and Macallum 10 who claim 

 that preparations made in that way may have a low phosphorus 

 content due to the cleavage of phosphorus from the casein mole- 

 cule by the action of the ammonia. In the preceding paper it 

 has been shown that this criticism does not hold. The analyses 

 of the preparations are given in the table. 



8 Bosworth. N. Y. Agrl. Expt. Sta. Tech. Bull. No. 31; also Journ. Biol. Chem. 

 15:236. 



9 Van Slyke and Bosworth. N. Y. Agrl. Expt. Sta. Tech. Bull. No. 26; also 

 Journ. Biol. Chem. 14:203. 



10 Harden and Macallum. Biochem. Journ. 8:90. 



