The Proteases of Plants (VI). 
BY 
S. H. VINES, F.R.S. 
Sherctrdian Professor of Botany in the University of Oxford. 
T HE latter part of my last paper (21) on this subject was devoted 
to an account of experiments upon ungerminated Hemp- seed 
(i Cannabis sativa ), made with the object of strengthening the evidence in 
favour of the view, to which I had given expression in several previous 
papers of this series, that ‘vegetable trypsin ’ is not, as is commonly held, 
a single substance, but is a mixture of at least two proteases. Of these, the 
one is only capable of peptonizing the higher proteins (fibrin, albumin, &c.) : 
the other has no action upon these proteins, but actively splits peptones 
and albumoses into amino-acids and other non-proteid nitrogenous sub- 
stances. That is to say, that ‘ vegetable trypsin 5 is a mixture of a peptase 
(peptonizing protease) with an ereptase (peptolysing protease), and possibly 
of more than one of each of these two kinds of enzymes. 
The method adopted in those experiments enabled me to prepare 
from Hemp-seed, solutions, of which some digested fibrin but were without 
action on peptones, that is, were merely peptonizing solutions ; others 
were without action on fibrin, but split up peptones (as indicated by the 
tryptophane-reaction) — that is, were merely peptolysing solutions. Thus 
it was shown that two distinct proteases, having different solubilities, can 
be extracted from Hemp-seed ; and there is no reason to doubt that these 
two proteases exist separately in the seed. 
Having obtained this result with Hemp -seed, I proceeded to apply 
the same method to various structures and substances, in the hope of 
obtaining confirmatory results ; but I soon found that it was only applicable 
to material which, like seeds, is rich in proteid substances. It became 
necessary, therefore, to find another method which should be of more 
general application ; and, as the result of many attempts, the method sought 
for was found in the course of some experiments with papain, as described 
in the following pages. 
Papain (or Papayotin). 
The latex of the Papaw ( Carica Papaya ) has long been known to act 
proteolytically. The first record of the digestive action is to be found 
in Griffith Hughes’s ‘Natural History of Barbados’ (1750) ; it is there 
[Annals of Botany, Vol. XXIII. No. LXXXIX. January, 1909.3 
B 
