CASEIN. 651 



amounts of lime-salts the paracasein-lime precipitates out while the 

 proteose-like substance (whey protein) remains in solution. In the 

 coagulation in an acid medium the conditions are entirely different and 

 proteoses and peptones are hereby formed to a considerable extent. 



The paracasein is very similar to casein, but cannot be recoagulated 

 by rennin. A solution of alkali-paracaseinate is much more readily 

 precipitated by CaCb than an alkali-caseinate solution of the same con- 

 centration, and the precipitation limits for saturated ammonium-sul- 

 phate solution, the upper as well as the lower limit, lie, according to 

 LAQUEUR, lower with paracasein than with casein. The internal friction 

 of paracasein solutions is also, in his opinion, less than that of casein 

 solutions and indeed even to 20 per cent. 



By continued action of rennin upon paracasein a further transformation 

 has been found in many cases (PETRY, SLOWTZOFF, v. HERWERDEN *). This 

 is explained by the presence of another proteolytic enzyme in the (impure) rennin 

 preparation. This assumption seems to be plausible, and we are here probably 

 dealing only with a secondary process which has nothing whatever to do with the 

 true formation of paracasein. Whey protein is also formed after the very short 

 action of rennin, and the continued cleavage occurs with varying speed. Thus 

 SCHMIDT-NIELSEN found that the quantity of whey protein was even 3 per cent 

 of the casein nitrogen after the action of rennet for 15 minutes, and only 4.25 

 per cent after 6 hours' action. These and other recent investigations favor 

 the assumption that the casein coagulation by rennet is a hydrolytic cleavage, 

 but the conditions are not so clear that this can be considered as proved. 2 



Fresh, unchanged milk does not, as is known, coagulate on boiling; but in 

 not too rapid action of rennin a state may be observed in which the milk coagu- 

 lates on heating (metacasein reaction). A solution of paracasein lactate, accord- 

 ing to LAX A, 3 coagulates with rennin the same as a solution of casein lactate, 

 which indicates, he believes, that the paracasein is transformed into casein again 

 by the lactic acid. But as a precipitation of the paracasein from the acid solu- 

 tion is perhaps a pepsin action, the transformation of the paracasein into casein 

 by the lactic acid must not be considered as proved. 



In the digestion of casein with pepsin-hydrochloric acid primarily a 

 phosphorized proteose is formed, from which then the pseudonuclein is 

 split off (SALKOWSKI). The quantity thus split off is variable, as shown 

 by the researches of SALKOWSKI, HAHN, MOBACZEWSKI, SEBELIEN, 

 and ZAiTSCHEK. 4 The amount of phosphorus in the pseudonucleins 

 obtained also varies considerably. SALKOWSKI considers that the quan- 

 tity of pseudonuclein split off is dependent upon the relation between 

 the casein and the digestion fluid, e.g., the quantity of the pseudonu- 



, Hofmeister's Beitrage, 8; Slowtzoff, ibid., 9; v. Herwerden, Zeitschr. f. 

 physiol. Chem., 52; W. van Dam, ibid., 61. 



2 See also Werncken, Zeitschr., f . Biol., 52. 



3 Laxa, 1. c. 



4 Salkowski, Zeitschr. f. physiol. Chem., 27; Salkowski and Hahn, Pfliiger's Arch., 

 59; Salkowski, ibid., 63; v. Moraczewski, Zeitschr. f. physiol. Chem., 20; Sebelien 

 ibid., 20; Zaitschek, Pfluger's Arch., 104. 



