418 



DILATOMETRIC METHODS 



by grinding 30 g. pig intestine with sand and 100 ml. 60% glycerol; 

 after filtering, 1:50 dilutions were made with phosphate buffers 

 having the different pH values and concentrations indicated in the 

 table. Controls were run in which the enzyme solution had been 

 heated at 100° for 30 min. in a sealed glass tube. 



TABLE IX 



Contraction Constants for Alanjdglycine Hydrolj^sis 



by Peptidase from Pig Intestine at Different 



pH Values and Phosphate Concentrations" 



" fi\./mM peptide bond. 



TABLE X 



Composition of Substrate for Peptidase Measurements 

 at Various pH Values 



Molarity of Molarity of 



pH DL-alanylglycine NaOH 



6.81 0.2 0.0100 



7.13 0.2 0.0193 



7.42 0.2 0.0346 



7.72 0.2 0.0611 



8.00 0.2 0.0900 



The deviations in the constants as determined by both methods at 

 pH 7.7 and 8.0 are not understood. Accordingly, Linderstr0m-Lang 

 and Lanz have chosen to limit the drop method, for the time being, 

 to reaction mixtures with pH values in the range 6.8 to 7.4. 



Enzyme experiments lasting 24 hours may be safely carried out. 

 The accuracy of the method is about fifty times that attained by the 

 microtitration procedure ( page 302 ) . An idea of the quantity of 

 material that may be subjected to investigation by the density gra- 

 dient method is given by calculations included in the paper of Lin- 

 derstr0m-Lang and Lanz. They estimated that if 10 hours be taken 



