HYDROGEN-ION CONCENTRATION 25 



Now it is clear that if we increase, say, H 2 in the above equation, then 

 in order that K may remain unchanged C 2 H 5 OOCCH 3 must diminish or 

 the substances which form the numerator of the equation must increase, 

 or both these changes must occur. As a matter of- fact, in such a case as 

 the above, both of these adjustments take place, for, as the ester breaks 

 down, it must thereby increase the concentration of acid and alcohol. 

 Since in aqueous solutions the reaction occurs in the presence of an excess. 

 of water, it is evident that the tendency for an ester in the presence of 

 water is to break down into alcohol and acid, and this must occur in all 

 reactions in the body fluids in which water enters into the equation. 



Physiological Applications. The application of the law of mass action 

 in the explanation of biochemical processes is very extensive. Most of 

 the reactions which enzymes or ferments are capable of influencing are 

 of the same general nature as that represented above, and the products 

 of their activities are usually the substances on the side of the equation 

 in which no water molecules appear i. e., they are hydrolytic reactions. 

 Enzymes merely accelerate the reaction (page 72), so that if we start 

 with a mixture of the substances on either side of the equation, all they 

 do is to -accelerate the production of a sufficient concentration of those 

 on the other side, until the equilibrium point is reached. For example, 

 an enzyme present in pancreatic juice, called lipase, accelerates the 

 breakdown of such esters as neutral fat, which consists of the triatomic 

 alcohol, glycerol, combined with the fatty acids palmitic (C 10 H 31 COOH), 

 stearic (C 17 H 35 COOH) and oleic (C 7 H 33 COOH): 



,C 3 H 5 (O OC C 17 H 35 ) 3 + 3H :! 0^3C ]7 H 35 COOH + C 3 H 5 (OH),. 



(the neutral fat, (the fatty acid, (glycerol) 



tristearin) stearic) 



Under ordinary conditions the reaction proceeds until nearly all the 

 neutral fat has become decomposed because of the preponderance of 

 water, but if we start with a mixture of fatty acid and glycerol with 

 just enough water to permit the enzyme to act, the reaction will pro- 

 ceed in the opposite direction i. e., so that some neutral fat will be 

 synthesized. This is called the reversible action of enzymes. 



Because of the universal presence of water, it is plain that such re- 

 versible reactions could not alone be held responsible for the synthe- 

 sis of neutral fat or of similar substances in the animal body. The only 

 way by which synthesis could occur under these conditions would be 

 if the substance produced along with the water were removed from the 

 site of the reaction as soon as it was formed. This might occur by the 

 precipitation of the substance or by its becoming surrounded by an en- 

 velope of some inert material. In the synthesis of neutral fat which 



