170 COMPOUNDS OF THE PROTEINS 



COMPOUNDS OF PROTEINS WITH OTHER PROTEINS. 



When the Protamines, which, it will be recollected, are strongly basic 

 proteins, are added to weakly alkaline solutions of other proteins, 

 precipitates are formed which consist of compounds of the protamine 

 and other protein employed. These compounds, once formed, are 

 tolerably stable, and when precautions are taken to prevent admixture 

 with excess of protamine they are found to be of very constant com- 

 position. These compounds were investigated by Hunter who found 

 that wiiile crystallized egg-albumin, casein, hemi-elastin, gelatin, 

 edestin, heteroalbumose, protalbumose, "alkali albuminate" and 

 histone sulphate yield a precipitate in alkaline solutions upon the addi- 

 tion of the protamine Clupeine. Elastin-peptone, deuteroalbumose histo- 

 peptone and several peptides fail to yield a precipitate. On digestion 

 of these precipitates with Pepsin the protamine is set free, since the 

 protamines are indigestible by pepsin, and the remainder of the 

 compound is converted into proteoses and peptones. 



The compound of Clupeine with casein contains six per cent, of the 

 protamine while the compound with hemoglobin contains five per 

 cent of protamine. The compound of Salmine with edestin contains 

 about ten per cent, of the protamine. 



When Globin and Casein are mixed in faintly acid solution a precipi- 

 tate of globin caseinate is formed which is soluble in excess of acid 

 or in dilute alkalies. The precipitate produced by admixture of an 

 excess of globin with sodium caseinate in solution contains about 34.5 

 per cent, of casein. A compound of globin with deuteroalbumose has 

 also been prepared by C. L. A. Schmidt. 



Thymus-histone combines with Hemoglobin, according to af Ugglas, 

 in the proportion of one part of thymus-histone to two of hemoglobin, 

 and with casein to form a compound containing about thirty per cent, 

 of histone. 



A particularly interesting compound protein is the Hemoglobin 

 Caseinate which has been prepared by af Ugglas. To a solution of 

 casein in alkali an excess of hydrochloric acid is added until the precipi- 

 tate of free casein which is at first formed is redissolved. The casein 

 hydrochloride is precipitated from this solution by the addition of 

 sodium chloride, and the precipitate redissolved and reprecipitated 

 until the washings from the precipitate are perfectly neutral. A 

 solution of this substance added to an excess of a solution of hemo- 

 globin produces a precipitate containing 33 per cent, of casein and about 

 66 per cent, of hemoglobin. The commonly accepted molecular 

 weight of hemoglobin, originally deduced from its content of iron, 

 and now confirmed by a variety of measurements, is about 16,700. The 

 minimal molecular weight of casein, calculated from the minimal 

 quantity of an alkali which will just carry it into solution (see p. 154), 

 is 8800. It seems evident, therefore, that casein and hemoglobin 

 combine with one another in molecular proportions. If the same is 



