i73 
Vines . — The Proteases of Plants {III). 
trypsin) than to the pepsin of animals. This view was further supported 
by Martin’s discovery (11) of leucin and tyrosin among the products of 
papain-digestion. On this ground Martin concluded that 4 papain is a 
proteolytic ferment acting almost exactly like trypsin.’ In a subsequent 
paper (12) Martin made the following interesting remark : 4 Why, indeed, 
there should be a pepsin-like ferment in some plants and a trypsin-like in 
others is as much a problem as why there should be the two forms in 
mammals.’ To what extent this problem has now been solved will appear 
in the sequel. In the meantime it may be generally asserted that the 
result of nearly all subsequent investigation has been to establish the 
4 tryptic ’ action of vegetable enzymes. Without quoting every individual 
case, it may be mentioned, for instance, that Green found (13) in the seed 
of the Lupin {L. hirsutus ) 4 a proteolytic ferment, working in an acid 
medium, capable of converting fibrin into peptone, leucin, and tyrosin.’ 
With regard to the protease of the Pineapple (. Ananas sativus ), Chittenden 
wrote (14) : 4 The results indicate that the ferment is more nearly related 
to trypsin than to pepsin, in that not only are proteoses and peptone formed 
by its action, but also leucin and tyrosin.’ In 1902 I summarized the 
conclusion to be drawn, as well from the researches of others as from my 
own, as follows (1, p. 19): — 4 The additional instances that I have now 
given of the production of tryptophane, selected as they are from various 
classes and from different parts of plants, bear out my previously expressed 
opinion that the proteolytic enzymes of plants in general are essentially 
44 tryptic.” This statement will at any rate hold good until definite evidence 
is adduced to prove the existence of a 44 peptic ” enzyme.’ 
The trypsin-theory was not, however, generally accepted without some 
demur. Thus Clautriau affirmed (15) that the enzyme of the pitcher-liquid 
of Nepenthes is a pepsin : but in my reply (16) I pointed out that this 
assertion must be incorrect, inasmuch as I had detected tryptophane 
among the products of Nepen //^-digestion. Again, Mendel and Underhill 
(17) made the statement that their observations indicate 4 that papain 
belongs to a class of enzymes which differs somewhat in type from the 
two proteolytic enzymes that have received most careful investigation in 
the past, viz. pepsin and trypsin. While the products of the papain- 
digestion of proteids resemble quite closely those of pepsin, so far as these 
have been examined in detail, the enzyme differs from ordinary animal 
pepsin in that it acts readily in both neutral and alkaline media. On the 
other hand, although papain is comparable with trypsin in exerting a 
solvent action in fluids of various reactions, the failure to form leucin, tyrosin, 
and tryptophane in appreciable quantities — at least under conditions in 
which they are readily formed in large quantities by other tryptic enzymes 
— places it in a class of its own for the present.’ In the course of special 
experiments to investigate these results (3, p. 605 ). I ascertained that the 
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