Mr Jackson, Molecular Weight of Glycogen. 115 



Molecular Weight of Glycogen. By Henry Jackson, M.A., 

 Downing College. 



[Received 14 March 1901.] 



In an investigation on the chemistry of glycogen it became 

 necessary to redetermine its molecular weight. The previous 

 results are those of Kiilz and Borntrager (Pf. xxiv. 19), who, by 

 noting the elevation of the boiling-point of water after introducing 

 a weighed quantity of glycogen, concluded that the formula was 

 (C 6 H 10 O 5 ) 6 . Sabaneff (J. Puss. Chem. Soc. 21) applying Raoult's 

 method of determining the molecular weight found a higher value, 

 viz. (C 6 H 10 O 5 ) 10 . 



All recent work has pointed to a more complex molecule than 

 either of these. The boiling-point method is not suited for very 

 complicated carbohydrates, and the glycogen used by Sabaneff 

 does not appear to have been completely free from mineral salts, 

 and the presence of small quantities of inorganic substances, soluble 

 in water, would increase the depression. 



It therefore became necessary to obtain the glycogen in a 

 state of purity, taking especial precautions to remove proteids 

 and mineral salts : the following method of preparation and puri- 

 fication was adopted, which is a slight modification of that described 

 by Lebben (Zeit. Oeffenth. Chem. 6). Horse liver was treated in 

 a porcelain dish with water and a little 15 per cent, potassium 

 hydroxide and boiled over wire gauze for 20 minutes. The extract 

 was filtered through glass wool, and was then precipitated with 

 80 per cent, alcohol. On the following day the precipitated crude 

 glycogen was collected on a filter and washed with alkaline 

 alcohol. 



For further purification the glycogen was dissolved in boiling 

 water and, when cold, was just neutralized with 10 per cent, 

 hydrochloric acid. To this solution dilute hydrochloric acid and 

 Brucke's reagent were added very carefully until no further pre- 

 cipitation of proteids occurred. Absolute alcohol was now added 

 until about 55 per cent, was present in the liquid. The pre- 

 cipitated glycogen was quickly filtered on the pump, washed with 

 absolute alcohol and finally with absolute ether. 



The glycogen, obtained as a white amorphous powder, was then 

 dissolved in water, and dialysed for a week. It was again pre- 

 cipitated with 55 per cent, alcohol and again subjected to dialysis. 



