826 



THE ROLE OF NITROGEN, ETC., I., 



racemic peptides were used, the hydrolysis took place on one-half 

 only of the racemic body. The cleavage of these simple 

 di-peptides gives us a clearer insight to the larger cleavage of 

 the protein-molecule, which is really constituted by the linking of 

 these simple units, the amino-group of one united to the carboxyl 

 group of the next. 



The investigations of Vines(88) have proved the presence in 

 plants of distinct peptoclastic enzymes. These belong, therefore, 

 to the group of erepsins which begin their work at the proteoses 

 and peptones. Considerable evidence has now accumulated to 

 show that in plants the proteoclastic enzymes are of the nature 

 of pepsin, while the hydrolysis is completed by various pepto- 

 clastic erepsins; and what we formerly regarded as trypsin is a 

 mixture of members of the peptic and ereptic groups of enzymes. 



Protein-transformation in germination, (a) Katabolinm. — It has 

 been repeatedly proved by experiment that the absolute amount 

 of nitrogen in seeds and their seedlings does not change; equiva- 

 lent weights of material therefore contain the same amount of 

 total nitrogen. The change in form of the nitrogen-compounds 

 during germination is illustrated by the following experiments of 

 Schulze.(89) 



Resting seeds 



3 days' seedlings 

 6 „ 



Q 



12 „ 

 16 „ 



18 „ 



Lupinus aiujustifolius. 



Protein N non-prot N 



92-89 % 



84-13 



48-31 



34-73 



28-67 



22-33 



22-78 



7-11% 

 15-87 

 51-69 

 65-27 

 71-33 

 77-67 

 77-22 



Zea Mays. 



Protein N non-prot. N 



97-95% 

 95-82 



91-62 

 85-30 

 66-67 



2-05% 

 4-18 



8-38 

 14-70 

 33-33 



per cent, of the total N 



In these two types of germinating seeds a great difference is 

 noticed in the rate of decomposition of the proteins. Schulze 

 explains this by the unequal enzyme-content of each. 



Let us examine the nature of the substances represented by 

 the second column of figures, in which it is seen that non-protein 



