THE INDIVIDUAL GROUPS OF PROTEINS 437 



Albumin (Ovalbumin). 

 Preparation. 



Ovalbumin remains in solution after the globulin has been precipi- 

 tated by half-saturation with ammonium sulphate. 



The filtrate is saturated with finely powdered crystals of ammonium sul- 

 phate. The precipitate is dissolved in water and again precipitated with 

 ammonium sulphate and the process is repeated several times. The last pre- 

 cipitate is dissolved in water and the solution is dialysed to remove the salt. 

 The albumin is obtained on evaporation in vacua at 40. 



Coagulated albumin is obtained by acidifying the solution and boil- 

 ing, washing the coagulum with water, alcohol and ether, and drying, 

 or by pouring it into several volumes of alcohol. The coagulum is 

 washed by decantation with alcohol and ether and dried. 



Preparation of Crystalline Ovalbumin (Hopkins]. 



Fresh egg-white is beaten into a froth with an exactly equal volume of 

 saturated ammonium sulphate solution and the mixture is filtered after stand- 

 ing for some hours. 10 per cent, acetic acid is added to the filtrate from a 

 burette with constant stirring until it becomes distinctly turbid, i c.c. of 

 acetic acid is then added for every 100 c.c. of filtrate. An amorphous pre- 

 cipitate is first formed, but on standing it becomes crystalline and with frequent 

 shaking the whole of the ovalbumin crystallises in 5-6 hours. After 24 hours 

 it is filtered off, washed with ammonium sulphate containing *i per cent, of 

 acetic acid and dissolved in water (i part in 10). Saturated ammonium sul- 

 phate solution is carefully added with gentle shaking until a permanent pre- 

 cipitate results, and then for every litre 2 c.c. more of ammonium sulphate. 

 The ovalbumin crystallises out and is washed as before. The crystalline mass 

 contains ammonium sulphate. A solution free from ammonium sulphate is 

 obtained by dialysis, or as above either in the uncoagulated or coagulated 

 condition. The yield is 50 gm. from 1000 c.c. of egg-white. 



Preparation of Conalbumin. 



The whole of the ovalbumin can never be obtained in a crystalline 

 condition. According to Osborne and Campbell only 50 per cent, of the 

 albumin can be crystallised. The remainder is termed conalbumin. It is 

 prepared from the filtrate by saturation with ammonium sulphate as described 

 under albumin. 



Properties. 



Ovalbumin in an uncoagulated state is an amorphous mass of a 

 yellowish colour, soluble in water and dilute salt solutions. It is not 

 precipitated from solution by saturation with sodium chloride, magnes- 

 ium sulphate or half-saturation with ammonium sulphate, but is pre- 

 cipitated by complete saturation with ammonium sulphate. 



A 2-5 per cent, solution in water coagulates at 60-64; in 10 per 

 cent, salt solution at 68-70. 



Conalbumin is very similar to ovalbumin, but it coagulates at a 

 lower temperature and has a higher rotation. 



The solutions of ovalbumin, crystalline ovalbumin and conalbumin 

 give all the general reactions for proteins. 



The coagulated albumins are insoluble in water and salt solutions, 

 but dissolve slowly in acid and alkali yielding solutions of derivatives 

 (metaprotein). 



