126 THE PROTEINS AND THE AMINO-ACIDS 



I. THE SIMPLE PROTEINS. 



Protamines. The protamines are the simplest proteins which are 

 as yet definitely known to occur in nature. They are found in sperma- 

 tozoa, and especially in the spermatozoa of fishes in combination with 

 nucleic acid, forming a simple type of nucleoprotein. They are pre- 

 dominantly basic substances, indeed so strongly basic that a solution 

 of salmine (the protamine from salmon spermatozoa) reacts alkaline 

 to litmus and absorbs carbon dioxide from the air, forming carbonates 

 of the protamine. The acid function of these substances is correspond- 

 ingly weak, although they are, like all proteins, amphoteric acids, and 

 in the presence of excess of strong bases will partially combine with 

 them. 



The protamines are soluble in water and form definite salts with 

 acids which are coagulated by alcohol and thrown out of solution 

 without decomposition, the combined acid being carried down quanti- 

 tatively with the protein. They yield a pink biuret-reaction resembling 

 in this respect the derivatives of the partial hydrolysis of other native 

 proteins. They yield, when completely hydrolyzed, a preponderating 

 proportion of diamino-acids. 



Histones. The histones are somewhat more complex and colloidal in 

 character than the protamines, and their basic function is less marked. 

 They are still predominantly basic, however, and occur, in cellular 

 tissues, combined with nucleic acid, and in the chromoprotein, hemo- 

 globin, combined with a colored acid radical, Hematin. They are 

 soluble in dilute acids or dilute solutions of the strong bases, but are 

 precipitated from acid solutions by the addition of ammonia. 



Albumins. The albumins are markedly colloidal substances which 

 are soluble in distilled water and in salt solutions. The basic function 

 is almost equal to the acid function. Representative examples are egg- 

 albumin and the albumin which is found in blood-serum. They are 

 coagulated by saturation of their solutions with ammonium sulphate. 



Globulins. The globulins are very decidedly colloidal substances 

 passing, for example, with difficulty, or not at all through clay filters. 

 They are insoluble in distilled water, but are soluble in dilute solutions 

 of strong acids or bases, or of inorganic salts. The acid function pre- 

 dominates slightly over the basic, so that they neutralize bases more 

 readily and completely than acids. Typical examples are afforded by 

 serum-globulin, the globulin which is precipitated from egg-white 

 by dilution with distilled water, and a variety of vegetable proteins 

 such as edestin, obtained from seeds -of hemp (Cannabis Sativa). They 

 are coagulated by half-saturation of their solutions with ammonium 

 sulphate or complete saturation with magnesium sulphate. 



Glutelins. The glutelins are a group of vegetable proteins of which 

 only two, the Glutenin of wheat and the Oryzenin of rice have as yet 

 been prepared in sufficient quantity, and purity to render analysis 

 and characterization possible. They are insoluble in water or dilute 



