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Proceedings of the Royal Society of Edinburgh. [Sess. 
produce this enzyme. A sterilised solution of sugar and Pepton Roche was 
made up and infected with a pure culture, and then incubated at 20° for 
several months. The development was, however, so small that it was 
quite impossible to carry out any examination of the mycelium, and no 
deposit of tyrosin appeared in the culture medium. 
The results obtained with the watery extracts of Saccharomyces are so 
slight that they must be regarded as being within the limits of experi- 
mental error. It is, however, possible that more active preparations could 
have been obtained by prolonged extraction or by addition of sodium 
chloride as suggested by Vines (Ann. Bot., vol. xviii. p. 289, 1904). The 
results are, however, in conformity with the statement made by that author, 
to the effect that a rapidly prepared watery extract of yeast has no proteoly- 
tic action, and with those of Geret and Hahn (Buchner, Die Zymasegdhrung , 
1903, p. 287) that the Buchner extract possesses a much stronger proteolytic 
action than that exhibited by the living yeast towards its substrate, and 
that the proteolytic and peptolytic activity is due to a cell enzyme. 
Whether this enzyme, as suggested by Geret and Hahn (l.c.), is of the 
nature of a tryptase has already been rendered doubtful by the works of 
Bokorny (Beihefte, Bot. Gentr., vol. xiii. p. 235, 1903), who suggested that an 
enzyme of the pepsin group is also present, and Vines (l.c.), who found 
evidence of the presence of an ereptase. 
In this connection, the results obtained with the Buchner extract 
(Extract B), which are shown in the preceding tables, are of interest. 
In the first place, it will be noticed that there is a strong peptolytic 
activity against Pepton Roche as well as against Pepton Witte. Secondly, 
the decomposition of Pepton Roche, as in the case of barley, is inhibited at 
50°, whereas the hydrolysis of Pepton Witte proceeds vigorously at that 
temperature. Thirdly, assuming the activity on Pepton Roche to be in- 
versely proportional to the time required for producing the first indication 
of tyrosin, this activity is, in the case of Saccharomyces, much more pro- 
nounced as compared with the action on Pepton Witte than in the case of 
barley, a fact which further supports the view of the non-identity of the 
two enzymes. Further, the proteolytic activity exhibited by the Buchner 
extract of Saccharomyces is very slight in comparison with the peptolytic 
activity, a fact which becomes even more striking when the results are 
compared with the corresponding figures obtained with Penicillium and 
Aspergillus. Finally, it would seem highly unlikely that the proteolysis 
and the peptolysis are catalysed by the same enzyme, as in that case the 
primary reaction would need to be accelerated in at least the same degree 
as the secondary one, which is obviously not the case. 
