io6 THE PHYSIOLOGY OF PROTEIN METABOLISM 



Autolysis. 



The body can make use of its stores of protein during starvation, 

 owing to the fact that each tissue contains proteolytic enzymes, 

 capable of bringing about a disintegration of the protein tissue, appa- 

 rently similar in every way to that produced by the action of pepsin, 

 trypsinand erepsin. It is more than probable that these enzymes play 

 an active part during the normal life of the organism, that they are 

 proteosynthetic as well as proteoclastic. For such a conception there 

 are many analogies ; take, for example, the proved reversible action of 

 maltase and of lipase, the work of Robertson (I.e.) and Taylor (l.c.) on 

 pepsin and trypsin, and the probable reversible action which goes on 

 in the liver, the conversion of sugar into glycogen, and of glycogen 

 back into sugar. Knoop (222) has also shown that the first phases 

 of the oxydative breakdown of amino acids in the tissues are reversible. 

 What are the peculiar conditions, then, under which this catabolic 

 function gains the upper hand in starvation? Is it because the 

 constitution and amount of the blood proteins are interfered with ? 

 Burckhardt (79), Lewinski (256), Gitken (153), Inagaki (206) have all 

 found a reduction in the amount of protein present in the blood in 

 lasting, the decrease being mainly in the albumin fraction. Hedin 

 (177) and Cathcart (87) have both shown that the serum possesses 

 active anti-proteolytic properties and that this anti-proteolytic action 

 is associated with the albumin fraction, thus it may be that the in- 

 creased autolysis in fasting is due in part to the disappearance of the 

 serum albumin. Schryver (362), on the other hand, holds that the 

 autolytic enzymes are held in check by purely chemical means. In 

 a series of experiments he demonstrated that a diminution of the 

 alkalinity of the tissues and fluids of the body from any cause was 

 followed by an increase in proteolytic activity. He found that acids, 

 especially lactic acid, accelerated the process of cellular disintegration. 

 The formation of acid, and particularly of lactic acid, is one of the 

 constant phenomena in autolysis. Mochizuki and Arima (286), Inouye 

 and Kondo (207), Frew (145), Turkel (402), Arinkin (54) have all come 

 to the conclusion that both organic and inorganic acids increase the de- 

 gree of autolysis in the liver. Schryver believes that the ammonia 

 arising from the breakdown of protein is largely responsible for main- 

 taining the protective alkalinity. The normal blood serum is not only 

 resistant to the action of trypsin, but is capable of inhibiting the normal 

 action of this enzyme on other proteins which are present, and which 



