38 THE BIOCHEMISTRY OF B VITAMINS 



Inositol 



The most widely recognized bound form of inositol is "phytic acid," 

 which has been obtained from plant sources in various states of cru- 

 dity many times, most often in the form of mixed salts. Posternak 89 

 synthesized the hexaphosphoric acid ester of inositol and gave good evi- 

 dence as to its identity with a natural material, but perusal of the litera- 

 ture shows that often the term "phytin" (supposedly an acid calcium 

 magnesium salt of phytic acid) has often been used uncritically for 

 material of indefinite composition. Other compounds, including lower 

 phosphoric esters and not agreeing in analysis with the classical formula, 

 have often been obtained. 90 - 91 The enzyme phytase, 92 which of course is 

 no more definite than its substrate, is present in plant materials and 

 catalyzes the hydrolysis of the inositol phosphoric esters. 



Inositol is also found in bound form in the phospholipide material. 

 Anderson 93 first found it in a phosphatide fraction from tubercle bacilli, 

 and Klenk and Sakai 94 obtained from the cephalin fraction of soybean 

 phosphatide a material which on hydrolysis yielded inositol and an 

 inositol monophosphoric ester. Folch and Woolley 95 obtained brain phos- 

 phatide fractions containing from 6.8 per cent up to 10 per cent inositol, 

 and Woolley 96 obtained a preparation from soybean, "lipositol," with a 

 content of 16 per cent inositol. Partial hydrolysis yielded inositol mono- 

 phosphate. An inositol galactoside linkage was thought to be present. 

 Complete hydrolysis yielded besides inositol, 15.5 per cent galactose, 8.3 

 per cent tartaric acid, 23.6 per cent oleic acid, cerebronic, palmitic and 

 stearic acids totalling about 21 per cent, phosphoric acid 9.8 per cent, and 

 ethanolamine. The content of the various fat acids and the analysis for 

 phosphoric acid indicate that the material is not a pure compound, though 

 the same conclusion holds for many refined phospholipide preparations. 



A third, and from the functional standpoint, highly significant form of 

 bound inositol is pancreatic amylase. 97 The purified enzyme not only con- 

 tains over 0.4 per cent inositol, but inhibition studies show that without 

 inositol the amylase cannot function. 98 * The implications of this finding 

 are far-reaching, especially if it should be found that starch- and 

 glycogen-splitting enzymes containing inositol are widespread. This might 

 account for the universal presence of inositol in living cells. 



The extraction of the total inositol from tissues in uncombined condi- 

 tion requires refluxing with 18 per cent HC1 for 6 hours. 99 A considerable 

 but variable portion can be extracted by milder procedures. Autolysis 10 ° 

 usually frees considerably less than does enzymatic treatment. 8 No criti- 

 cal study has been found recorded of the way inositol may be released 

 * See footnote p. 10. 



