IN LIVING MATTER 33 



In a similar fashion, Hanriot showed that lipase is capable 

 of forming mono-butyrin from butyric acid and glycerine. 



In so far, however, as the syntheses of simple esters by lipase 

 are considered to have a bearing upon the synthesis of neutral 

 fats by the same enzyme in the body, it must be pointed out that 

 the reactions are of somewhat different type, and that the 

 equations of equilibrium, taken in conjunction with the solu- 

 bilities of the neutral fats, show that the synthesis of neutral fats 

 is a much more difficult process, and one which, granted that it 

 may occur by reversed action of the enzyme under the conditions 

 existing in the cell, is exceedingly unlikely to occur in aqueous 

 solution in the test-tube. 



The difference arises from the fact that the two syntheses 

 achieved by the authors mentioned above of ethyl-butyrate, and 

 mono-butyrin, are produced in reactions in which single mole- 

 cules of each of the constituents unite to form a molecule of the 

 ester ; while in the case of the neutral fats three molecules of 

 the fatty acid concerned unite with one molecule of the glycerine. 

 If we represent the osmotic pressures (which are proportional 

 to the molecular concentrations) by P E , P A , and P B , for ester, acid, 

 and base respectively, then the equation of equilibrium for the ethyl- 

 butyrate and mono-butyrin becomes P E = K.P A .P B or P E = K . P 2 A , 

 and that for the neutral fat is P E = K . P 3 A . P B , or, assuming that 

 the constituents are present in the proper concentrations for 

 combination, P E = K . P 4 A . 



Contrasting the two formulae P E = K . P A 2 and P E = K . P A 4 , 

 we see that in the case of such a reaction as that in which a 

 neutral fat is formed, the tendency to remain dissociated in 

 dilute solution, and to remain combined in concentrated solution 

 are more exaggerated than in the simpler reaction. Accordingly, 

 as we pass from a concentrated solution to a dilute solution the 

 value of P E falls very rapidly compared to the fall in P A , or the 

 relative amount of neutral fat becomes very small. In excessively 

 concentrated solution practically all would be neutral fat, but 

 very rapidly on reducing the concentration nearly all would be 

 hydrolysed to free fatty acid and glycerine. 



Hence a synthesis of neutral fat from fatty acid and gly- 

 cerine is only possible in a highly concentrated solution. 

 But the physical property of the fatty acids and neutral fats 



