284 



Report of the Department of Chemistry. 



A molecule of calcium casemate containing four equivalents of 

 base is split by rennin into two molecules of paracaseinate, each con- 

 taining two equivalents of base. Such a paracaseinate is soluble 

 in pure water but insoluble in the presence of more than a trace of 

 a soluble calcium salt. A molecule of calcium caseinate containing 

 two equivalents of base is split by rennin into two molecules of 

 paracaseinate each containing one equivalent of base. Such a para- 

 caseinate is insoluble in pure water. 



The small amounts of nitrogen recovered in the filtrates in the 

 experiments given above may be due to autohydrolysis or to pro- 

 teolysis produced by the pepsin in the rennin extract used, as is 

 indicated by the following experiment. 



Into each of several flasks were placed 50 cc. of a casein solution 

 and a little toluol. One-half of the flasks received a few drops each 

 of rennin solution, the others being kept as controls. The contents 

 of the flasks were examined at intervals for autohydrolysis and 

 proteolysis. The nitrogen in the control flasks which was not pre- 

 cipitated by acetic acid was considered as due to autohydrolysis; 

 while in the case of the other flasks the nitrogen not removed by 

 filtering was considered to be due to autohydrolysis and proteolysis. 

 By subtracting the nitrogen found in the controls from those con- 

 taining rennin a fair idea as to the extent of the proteolysis might 

 be obtained. 



12 hours 



Milligrams of nitrogen in original solution as casein 



Milligrams of nitrogen in filtrate from rennin flasks 



Milligrams of nitrogen in filtrates from control autohydrolysis, 

 Milligrams of nitrogen due to proteolysis 



158 

 18.2 

 2.1 

 16.1 



Solutions of ammonium, sodium or potassium caseinates contain- 

 ing two or more equivalents of base could not be coagulated by 

 rennin, but the subsequent addition of calcium chloride caused 

 coagulation, the curd being calcium paracaseinate. That sodium 

 caseinate in solution was changed to sodium paracaseinate was 

 shown by the following experiment. Rennin was added to a solu- 

 tion of sodium caseinate and after a short time acetic acid was added. 

 The precipitate, after being purified and dried, was found to be 

 paracasein. 



In conclusion I wish to express my appreciation of the interest 

 in this work shown by Dr. L. L. Van Slyke, of the Chemical Lab- 

 oratory of the New York Agricultural Experiment Station, Geneva, 

 N. Y., and Dr. Otto Folin of the Biochemical Laboratory of the 

 Harvard Medical School, Boston, Mass. 



