The Proteases of Plants (III). 
BY 
S. H. VINES, F.R.S., 
Sherardian Professor of Botany in the University of Oxford. 
I N the series of papers (Nos. 1 - 5 ) that I have contributed during the last 
three years to the Annals of Botany, I have given the results of a large 
number of experiments which suffice to prove that proteases are very 
widely distributed both in the body of the individual plant and in the 
vegetable kingdom : so widely, indeed, that further investigation may be 
expected to show, in the course of time, that they are present in every 
part of every plant at some stage or other of its development. 
With regard to the nature of the proteases, I have shown that they 
are not, as had been previously thought, necessarily such as can act upon 
the higher proteids (fibrin or albumin). Though I have been able to add 
to the number of the plants whose juices can effect fibrin-digestion (see 5 , 
p. 161), a more important contribution to the knowledge of the subject 
is the discovery of a protease which is without action on the higher 
proteids but proteolyses the simpler proteids, notably albumoses and 
peptones, as indicated by the application of the tryptophane-test ( 2 , p. 2562). 
This protease thus belongs to the group of the ereptases, finding its nearest 
analogue in the erepsin of the animal body : but with this difference, that 
whilst animal erepsin is most active in a slightly alkaline medium, the 
erepsin of plants is most active in a slightly acid medium (see 4 , p. 314). 
The erepsin is of more general occurrence in plants than the protease that 
digests fibrin ; as is shown by the fact that in many cases the juices or 
prepared extracts of different parts of various plants that were found to 
proteolyse albumoses or peptones actively had no digestive action on 
fibrin. No case was, however, observed of the digestion of fibrin, whether 
by the juice, an extract, or the tissue of a part of a plant, without the 
occurrence of tryptophane among the products. In other words, whilst 
peptolysis can take place without fibrin-digestion (peptonization), fibrin- 
digestion has not yet been found to take place without peptolysis. This 
justifies the statement that the peptolytic enzyme may occur independently, 
whereas there is no evidence of the independent existence of a purely 
[Annals of Botany, Vol. XIX. No. LXXIV. April, 1905.] 
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