CHEMISTRY: K. G. FALK 
559 
Inactivation by salts. — The action of salts on these enzymes has 
already been described. Some produced marked inactivation, others 
less, while some accelerated the hydrolytic actions. 
Inactivation by heat. — ^Like all enzymes, the esterase and lipase are 
both inactivated by heating their aqueous solutions or suspensions for a 
few minutes at 100°. The original oil-free and husk-free castor beans, 
on being heated dry at 100-110° lost 50-80% of their lipolytic activity; 
the same loss of weight in a vacuum desiccator over phosphorus pen- 
toxide was not accompanied by loss in activity. Drying first, and then 
heating (the latter causing only 0.1-0.2% greater loss in weight) pro- 
duced 50-80% loss in activity. 
Nature of the chemical changes involved in the inactivations . — The sum- 
mary of the different ways in which the esterase and lipase preparations 
may be inactivated makes it appear at first sight as if different reac- 
tions occurred in the inactivations. If, however, a definite chemical 
group is responsible for a definite enzyme action, it might perhaps be 
more reasonable to assume that inactivation followed a definite reac- 
tion. The preparations were essentially protein in character. There 
is no evidence that a dehydration, or loss of the elements of water, 
causes the inactivation. Some of the reactions indicate that a possible 
hydrolysis may be a cause of inactivation. With proteins, hydrolysis 
is generally taken to occur with the — CO-NH — group, which goes 
over into the — COOH NH2 — groups. Experiments with all the in- 
activations showed in no case an increase in the formal titration as 
would be expected in such a reaction, and therefore makes the assump- 
tion of such a hydrolysis improbable. Coagulation of the material 
accompanied some of the inactivations. This physical change alone 
does not appear satisfactory as an explanation, some change in chemi- 
cal structure unquestionably accompanying or producing the physical 
phenomenon. Furthermore, the lipase material in suspension in water 
showed the same activity as in 1.5 normal sodium chloride solution 
when tested immediately. 
The explanations of the chemical changes accompanying inactiva- 
tion so far suggested are not satisfactory. The reagents used are 
simple. It is difficult to conceive of a very deep-seated chemical reac- 
tion taking place under so many different conditions, none of a com- 
plex nature. To the writer the only chemical change which appears 
probable under these conditions is that involving a simple rearrange- 
ment within the molecule, such as a tautomeric change involving the 
change in position of a hydrogen atom. In considering the structure 
