5 
Vines . — The Proteases of Plants ( VI ). 
The foregoing experiments demonstrate the isolation from papain, by 
this method, of a solely peptonizing enzyme, peptase, in the form of an active 
NaCl.-solution. It is clear, however, that a great deal of this enzyme 
is lost in the preliminary treatment of the papain with 20-25 times its bulk 
of 2 per cent. NaCl-solution : for, as stated above, this first extract actively 
digests fibrin. This consideration led me to devise a supplementary 
method which makes use of this extract, as explained in the following 
experiment : — 
10 grms. of ‘ raw papain ’, merely the dried latex as imported, were ground to 
powder, and were well triturated with 150 cc. of 5 per cent. NaCl-solution : the mix- 
ture was placed on a filter, and the filtrate dropped into 300 cc. of alcohol, where a 
dense ppt. was formed. The ppt. was then collected on a filter : it was subsequently 
extracted with 200 cc. of distilled water, and the mixture was put on a filter. 
Filtrate 1. The filtered H 2 0 -extract is of a brown colour, the colour having 
developed during filtration ; it is clear and neutral ; it gives ppt. on boiling, dense ppt. 
on adding HN 0 3 , and strong xanthoproteic reaction : a portion of it, boiled and 
filtered, gives good biuret-, but no tryptophane-reaction. 
Digestive properties. The filtrate was found to digest both fibrin and Witte-peptone 
within eighteen hours. 
The residue was now extracted with 100 cc. 2 per cent. NaCl-solution, and the 
extract filtered. 
Filtrate 2. The filtered NaCl-extract was clear, colourless, neutral, gave a tur- 
bidity on boiling and on adding HN 0 3 , and a distinct xanthoproteic reaction : a 
portion of it, after being boiled and filtered, gave no biuret- or tryptophane-reaction. 
Digestive properties. The experiment is worth giving in full. 25 cc. of the filtrate 
were put into each of four bottles, the liquid put into No. 2 having been previously 
boiled ; to each bottle were added 0*2 grm. fibrin and the same quantity of Witte- 
peptone ; to No. 3 citric acid was added to 0-3 per cent. ; and to No. 4, HC 1 to 
005 per cent. 
After twenty-fours’ digestion, the fibrin had disappeared in No. 1 (neutral) ; it 
was unaltered in No. 2 (boiled) and in Nos. 3 and 4 (acid), and remained so during 
twenty-four hours’ further digestion. No tryptophane-reaction was given by the con- 
tents of any of the bottles. 
Hence the solution contained only a fibrin-digesting enzyme, the action of which 
was arrested by acidity. 
Thus the results obtained by the investigation of the NaCl-extract of 
papain agree with those obtained by the investigation of the papain-residue. 
The material used in these experiments was chiefly what is known as 
‘ Commercial Papain ’ ; the more important results were verified by experi- 
ments with ‘ Raw Papain ’ — that is, the dried latex as imported, kindly 
supplied to me by Messrs. Thomas Christy & Co., of London. 
It was thus shown that the digestive properties of the latex, as here 
described, are not due to, nor are materially affected by, the processes of 
purification by which commercial papain is prepared from the raw latex. 
