COENZYMES DERIVED FROM B VITAMINS 127 



identical with human pancreatic amylase. Inositol analyses on these 

 preparations have not been reported, nor is information on the inositol 

 content of saliva available. 



Inositol, according to indications, has two possible biological functions 

 independent of the one just described. It is a component of certain phos- 

 pholipides (Section D), and may be an important factor in the regulation 

 of fat metabolism in mammals. It is impossible to give clear presentation 

 of the latter function because of disagreements which have not yet been 

 resolved concerning the manner in which dietary factors influence the pro- 

 duction of fatty livers. The confusion one encounters in attempting to 

 follow the literature is due to several facts: different investigators have 

 used different means of producing fatty livers; the types of lipides de- 

 posited have not always been well characterized; and it has been neces- 

 sary to use crude liver extracts rather than pure substances to supply 

 certain vitamins. 7 - 8> 9 



"Lipocaic" was the name given to an uncharacterized heat-stable sub- 

 stance (s) present in pancreas which was effective in preventing the fatty 

 livers induced by diets containing liver extracts of high biotin content. 

 Inositol, at one time, was claimed to be an active component of lipocaic, 

 but its activity apparently is not as great as once believed and inositol 

 per se is not as effective as choline. 10 



Another lipotropic factor, protein-like in nature, obtained from the 

 pancreas will prevent the fatty liver which results from pancreatectomy 

 of dogs. This type of fatty liver can also be treated by adding choline to 

 the diet. It is believed that the protein-like lipotropic factor functions 

 by catalyzing during digestion certain hydrolytic reactions which are 

 necessary to liberate methionine and choline from food, and that these 

 compounds are the actual agents which prevent the abnormal deposition 

 of fat in the liver. 11 Apparently no effort has been made, however, to 

 determine if the lipocaic action of inositol may be due to its presence in 

 the lipotropic protein of the pancreas. If appreciable amounts of inositol 

 were found in the more active preparations, it would be indicative that 

 inositol is a component of another hydrolytic enzyme produced by the 

 pancreas. 



Hydrases and Isomerases 



A class of reactions distinct from the synthetic and hydrolytic processes 

 just discussed is the intramolecular hydrations and dehydrations — reac- 

 tions in which the elements of water are added to or removed from a single 

 molecule. A number of essential steps in the metabolism of carbohydrates 

 and fats are of this type: fumaric acid ^± malic acid; phosphogly eerie 

 acid ^± phosphopyruvic acid ; /3-hydroxybutyric acid ±=> crotonic acid (p. 



