298 
Vines . — The Proteases of Plants. 
investigation in this direction than that of Naegeli (10), who stated the 
proteid content of yeast containing 8 °/ o of nitrogen as follows : — 
Ordinary albumin ..... 36 °/ o . 
Gluten-casein, soluble in alcohol . . . 9 „ 
Peptone, precipitated by lead acetate . . 2 „ 
This statement is not altogether clear. The first item probably 
means that 36 °/ o of the dry weight of the yeast consisted of coagulable 
proteid. The significance of the second item is doubtful : it is not im- 
possible that it may really be albumose, or perhaps a mixture of albumoses 
and peptones. For some albumoses are relatively soluble in alcohol, 
precipitation only beginning with an alcoholic strength as high as 80 °/ o ; 
moreover, some of them possess the property, specially mentioned as 
characteristic of Naegeli’s ‘ gluten-casein,’ of readily giving off sulphuretted 
hydrogen when treated with caustic soda or potash. Again, peptone 
is to some extent soluble in alcohol when at all dilute ; in fact one 
form (amphopeptone B) of it is soluble in 9 6°/ o alcohol. Finally, the 
substance described as 4 peptone, precipitated by lead acetate,’ is possibly 
not 4 peptone ’ at all, since peptone proper (amphopeptone) is only partially 
precipitated by lead acetate : it is more probably one of the albumoses 
which are readily precipitated by this reagent. 
In view of the rapidity with which autolysis took place, as indicated 
by the tryptophane-reaction, it seemed probable that the dried yeast used 
in my experiments contained albumoses or peptones, or a mixture of these, 
to begin with ; and I have only so far investigated the proteids as to 
determine this point. A filtered watery extract was slightly acidulated and 
then boiled, when a precipitate of the coagulable proteids (albumin, &c.) 
was obtained. The filtrate was concentrated by evaporation and then 
treated with excess of alcohol, when a considerable precipitate was given. 
The precipitate was filtered off, dried, and dissolved in water on a filter ; 
the solution was then saturated with ammonic sulphate, after the method of 
Kiihne, in both alkaline and acid reaction, giving a considerable precipitate 
which consisted of albumoses. The filtrate, after appropriate treatment, still 
gave the biuret-reaction, indicating the presence of amphopeptone. Hence 
it is clear that the dried yeast contained both albumoses and peptones, the 
former in larger quantity than the latter. What still remains to be done 
is to determine the nature of the proteids that are coagulated on boiling. 
Since there is evidence that the dried yeast contained albumoses and 
peptones, and since the test of proteolysis was the presence of tryptophane, 
my experiments do not throw light upon the peptonization of the higher 
proteids of the yeast in the course of autolysis. The conclusion to be 
drawn from them is that there is present in yeast a peptolytic enzyme 
which is most active at or near the natural acidity of a watery mixture 
or extract, which is due to the presence of acid phosphates. 
