PREPARATION OF GLYCOGEN 113 



The following method has recently been described by 

 Harden and Young * : The yeast is ground with an equal 

 weight of sand. It is then extracted by boiling with water, 

 and an equal volume of alcohol added to the cooled and 

 filtered liquid. The precipitate formed is collected, washed 

 with 50 per cent alcohol, and is then treated on the boiling 

 water bath with a 60 per cent solution of potassium hydroxide 

 for two hours. The liquid is cooled and poured into an equal 

 volume of water, filtered, and the filtrate precipitated by the 

 addition of two volumes of alcohol. The precipitate is col- 

 lected, and washed repeatedly with a mixture containing 

 400 c.c: of water, 100 c.c. of 50 per cent potassium hydroxide, 

 and 500 c.c. of alcohol ; it is finally washed with 50 per cent 

 alcohol. 



The precipitate is then dissolved in water, and the solu- 

 tion, which is alkaline owing to the difficulty of washing away 

 all the potassium hydroxide, is neutralized with acetic acid, 

 and the glycogen precipitated by the addition of an equal 

 volume of alcohol. By repeatedly dissolving in water, and 

 reprecipitating with alcohol, a preparation may be obtained 

 free from nitrogen and ash, but it still contains yeast-gum, 

 which may be removed by redissolving the crude glycogen in 

 water and saturating with ammonium sulphate. The pre- 

 cipitated glycogen, after being washed with saturated am- 

 monium sulphate, is dissolved in water, and the solution again 

 saturated with ammonium sulphate, the process being repeated 

 three times. The final precipitate is again dissolved, the 

 solution dialysed until free from ammonium sulphate, and the 

 glycogen precipitated with alcohol. For details of the further 

 purification of the glycogen the original paper should be 

 consulted. 



Properties. 



Pure glycogen is a snow-white amorphous solid. It is 

 readily soluble in hot water, forming an opalescent solution, 

 from which it may be precipitated again by alcohol, provided 

 small quantities of dissolved salts are present; 100 c.c. of a 

 I per cent solution when mixed with 200 c.c. of absolute 



* Harden and Young: " J. Chem. Soc.." 1912. 101. 1928. 

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