wheat bran, believed that a part of it existed as inosite tetraphosphoric 

 acid, but no definite compound of this composition was isolated. 



As previously mentioned, Rather (1918) in an extensive series of 

 investigations disputes the existence of inosite hexaphosphoric acid 

 in any plant material. All of the preparations which he obtained were 

 regarded as salts of inosite pentaphosphoric acid, C e H„ (OH) 

 (P0 4 H„)-, or of a hypothetical acid having the formula C 12 H 41 4 .,P 9 . 



As a result of our studies we believe that the whole series of pos- 

 sible esters of inosite and phosphoric acid exists ; viz., inosite hexa-, 

 penta-, tetra-, tri-, di- and monophosphoric acid. We believe, however, 

 that the lower esters are formed by hydrolysis through enzymes, acids 

 or through spontaeous decomposition of a mother substance which is 

 inosite hexaphosphoric acid. Judging by our experience, the lower 

 esters are always obtained as mixtures and it is extremely difficult to 

 separate them. The amorphous barium salts of such lower esters as 

 the inosite di- and triphosphoric acids are comparatively soluble in 

 cold water and may, therefore, be removed from the higher inosite 

 tetra-, penta- or hexaphosphoric acids with a fair degree of complete- 

 ness by repeating the operation of extraction with cold water several 

 times. In like manner, it is possible to effect a partial separation of 

 inosite di- and triphosphoric acids from a mixture of these two com- 

 pounds, but it is practically impossible to separate completely the two 

 substances by this method. 



When these esters occur in conjunction with inosite hexaphos- 

 phoric acid, as they may frequently do when isolating the latter sub- 

 stance from plant material in which the enzyme phytase exists, it is very 

 difficult to remove the lower esters completely and obtain compounds 

 which give results on analysis corresponding to salts of inosite hexa- 

 phosphoric acid. 



While we do not doubt the existence of all of these esters, as stated 

 above, we do not believe that experimental evidence has been presented 

 sufficient to prove the existence of more than the following: 



Inosite hexaphosphoric acid. 



Inosite tetraphosphoric acid (synthetic). 



Inosite triphosphoric acid. 



Inosite monophosphoric acid. 



As has already been mentioned, it has been observed that very 

 carefully purified preparations of inosite phosphoric acid from different 

 sources, either the crystalline barium salt or the free acid, undergo 

 spontaneous decomposition with the gradual liberation of inorganic phos- 

 phoric acid and the production of lower phosphoric acid esters of 

 inosite. This process is very much hastened by the enzyme phytase in 

 aqueous solutions under proper conditions of temperature and acidity. 

 Evidently the same reactions do not occur in the dry plant material. 



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