474 EFFECT OF ENZYME ON DIGESTION OF PROTEINS 



of the reaction. If the amount of egg albumin and all other factors 

 except the amount of pepsin are kept equal, however, the time neces- 

 sary to cause a given change may be considered as a definite measure 

 of the rate of reaction, which is all that is necessary for the present 

 purpose. 



It was stated^ that the rate of reaction (i.e. the reciprocal of the 

 time to cause a given change) was directly proportional to the con- 

 centration of enzyme solution, and that any products of reaction 

 present in the enzyme solution did not interfere with the reaction. 

 Both statements were true as regards the pepsin solutions used in 

 the experiments reported. It was found, however, that some pep- 

 sin solutions did not obey this law. The rate of digestion, instead 

 of being directly proportional to the enzyme concentration, increased 

 much more slowly. The same phenomena have been observed by 

 Bayliss in the case of trypsin^ and invertase,^ and have frequently 

 been observed in enzyme reactions. It has formed one of the argu- 

 ments for the conception that the enzyme combines with the substrate 

 according to the adsorption formula. ^'^ 



Table I is a summary of an experiment illustrating this point. 

 The results are shown graphically in Fig. 1. It is obvious that the 

 value of ET (total pepsin concentration X the time necessary to 

 cause 10 per cent of the total change in conductivity) is constant for 

 low concentrations but increases in higher concentrations. (If the 

 rate of reaction is directly proportional to the enzyme concentration, 

 the value of ET must of course be constant.) The calculated figures 

 were obtained by a formula considered below. The key to this be- 

 havior is given by the results of the experiments shown in Table II. 

 In this experiment 2.5 cc. of an active pepsin preparation were diluted 

 to 10 cc. A, with HCL (pH 2.0) and, B, with a solution of " peptone "i° 

 prepared by the digestion of egg albumin by a very small amount of 

 pepsin (but containing no active pepsin). Solutions A and B were 



' Bayliss, W. M., Arch. Sc. Biol, 1904, ii, suppl., 261. 



8 Bayliss, W. M., Proc. Roy. Soc. London, Series B, 1911-12, Ixxxiv, 90. Du- 

 claux, E., Chimie Biologique, Paris, 1883. 



^Bayliss, W. M., The nature of enzyme action, Monograph on Biochemistry, 

 London, New York, Bombay, and Calcutta, 3rd edition, 1914. 



'"The word peptone is used in this paper as a general term for substances 

 with which pepsin combines in solution, but does not hydrolyze. 



