BY JAMES M. PETRIE. 825 



being split into simpler and soluble substances fit for trans- 

 location. 



Enzymes. — The protein-splitting enzymes of plants have been 

 divided into three groups according as they partake of the nature 

 of the pepsin, trypsin, or erepsin of animal juices. Considerable 

 difficulty was met with in identifying the true nature of these; 

 it was usual to describe as peptic those enzymes which acted only 

 in acid solution, while tryptic enzymes worked in alkaline 

 solutions. But some are active in both, others are destroyed by 

 both acids and alkalies, and others again act only in presence of 

 very weak organic acids. Now all these difficulties are vanishing 

 in the light of Fischer's work, for none of his synthetic polypep- 

 tides (conjugated amino-acids) have as yet been split by pepsin,, 

 while they are rapidly decomposed by the pancreatic enzymes. 

 This has caused a complete revision of the classification of plant- 

 enzymes, in which the work of Abderhalden stands out con- 

 spicuously. A specially favourable peptide for this purpose is 

 glycyl-1-tyrosin, an optically active compound of the two amino- 

 acids. When split, its components are easily demonstrated by 

 the insolubility of tyrosin and the HCl-ester of glycin, while the 

 method of proving the unchanged dipeptide is very definite and 

 certain. Further, the strong rotation in the polariscope is 

 rapidly negatived if cleavage takes place, as the simple amino- 

 acids are optically inactive in water-solutions; this change of 

 the rotation is seen immediately on commencement of hydrolysis. 



Abderhalden(87) has used glycyl-gly'cin, glycyl-tyrosin, leucyl- 

 glycin, etc., and has shown that the endotryptase of yeast is a 

 tryptic ferment, so also is papain; while on the other hand with 

 juice of Nepenthes, which, in its pitchers, is capable of digesting 

 meat in a neutral solution, almost no hydrolysis took place; it is 

 therefore not of the nature of trypsin. Abderhalden has also 

 studied the effect of the proteoclastic ferments of germinating 

 seeds on the polypeptides, by bruising the seeds in a mortar with 

 sand, and expressing the juice under three hundred atmospheres 

 pressure. All the polypeptides tried were split by the press- 

 juice from seedlings of legumes and cereals; and, further, when 



