104 THE PROTEIN SUBSTANCES. 



It is just as difficult to draw a sharp line between the globulins and 

 albuminates as it is between the globulins and albumins. Several globu- 

 lins are very readily changed by the action of very little acid, as also by 

 standing under water when in a precipitated condition, into albuminates, 

 and then become insoluble in neutral salt solutions. OssoRNE, 1 who has 

 closely studied this property in connection with edestin (from hemp-seed) , 

 considers the globulin, " globan," which has been made insoluble in salt 

 solution, as an intermediate step in the formation of the albuminate which is 

 produced by the hydrolytic action of the H ions of water or of the acid. 



Phosphoproteins are a group of phosphorized proteids which occur 

 extensively in the animal and plant kingdoms and which include the 

 nucleoalbwnins and the little-studied lecithalbumins. 



Nucleoalbumins. These proteids behave like rather strong acids r 

 are nearly insoluble in water, but dissolve easily with the aid of a little 

 alkali and, in the entire absence of phosphatides, contain also 

 phosphorus. Certain of the nucleoalbumins, resemble the globulins by 

 their solubility and precipitation properties. Others resemble the 

 albuminates, but differ from both of these groups by containing phos- 

 phorus. They stand close to the nucleoproteins by their content of 

 phosphorus, but differ from these in not yielding any purine bases on 

 cleavage. It has not yet been found possible to obtain from the neucleo- 

 albumins any proteid-free pseudonucleic acids corresponding to the 

 nucleic acids, but only acids rich in phosphorus, which always give the 

 proteid reactions. 2 For this reason the nucleoalbumins cannot be classed 

 as compound proteins. In peptic digestion a proteid rich in phosphorus 

 can be split off from most nucleoalbumins, and this has been called 

 para- or pseudonuclein. The claim made that the pseudonuclein is a 

 combination of proteid with metaphosphoric acid has been shown to be 

 incorrect by the investigations of GIERTZ. S 



! The separation of pseudonuclein in peptic digestion is no doubt characteristic 

 of the nucleoalbumin group, but the non-appearance of the pseudonuclein pre- 

 cipitate does not entirely exclude the presence of a nucleoalbumin. The extent 

 of such a formation is dependent upon the intensity of the pepsin digestion, the 

 degree of acidity, and the relation between the nucleoalbumins and the digestive 

 fluids. The separation of a pseudonuclein may, as shown by SALKOWSKI, 

 not occur even in the digestion of ordinary casein, and WR6BLEWSKI and others 4 

 did not obtain any pseudonuclein at all in the digestion of the casein from human 

 milk. The most essential characteristic of this group of proteids is that they con- 

 tain phosphorus, and that the purine bases are absent in their cleavage products. 



1 Zeitschr. f. physiol. Chem., 33. 



2 Levene and Alsberg, ibid., 31; Salkowski, ibid., 32; Levene, ibid., 32; A. Reh, 

 Hofmeister's Beitrage, 11; Dietrich, Bioch. Zeitschr., 22. 



3 Giertz, Zeitschr. f. physiol. Chem., 28. 



4 Salkow8ki, Pfliiger's Arch., 63; Wr6blewski, Beitrage zur Kenntnis des Frauen- 

 kaseins, Inaug.-Diss., Bern, 1894. 



