AMINO ACIDS AND DERIVATIVES IN DROSOPHILA I45 
It should again be emphasized that these data are not very accurate and that this 
is not a random sample of the peptides of Drosophila. We expect to provide more 
extensive and satisfactory information in the near future by use of a Spinco Amino 
Acid Analyzer although we have not entirely solved the problem of obtaining pure 
peptides in large numbers. 
DISCUSSION 
At the outset of this work, some 5 years ago, we expected to find in Drosophila a 
variety of free amino acids and perhaps as many as ten peptides and other amino acid 
derivatives as the pool from which proteins could be made. That the situation is nearly 
100 times this complex could not have been predicted from earlier work on other 
organisms although numerous more recent reports have presented evidence for the 
existence of considerable numbers of peptides in yeast and bacteria (see review by 
J. HoLpEN in this Symposium). Although these reports and our own qualitative 
observations have indicated to us that the picture in Drosophila is not unique, we 
have applied our methods to materials other than fly tissue to a very limited 
extent. 
One example is summarized in Fig. 8 and, although the column elution system 
was designed only for separation of acidic substances, some interesting conclusions 
can be drawn. The material placed on the column was obtained by the procedure 
described here as Fraction 1 (Fig. 4) froma 9-g, fresh rabbit brain. The data are plotted 
at three levels of concentration to show relative amounts of components. By paper 
chromatography of such an extract one would see only the components of the two 
larger peaks shown in the top graph. Nevertheless, as shown in the bottom graph, 
all the tubes from elution contain one or more components and many are peptides. 
Therefore, rabbit brain also contains a great variety of ninhydrin-reacting components 
but the concentrations of most are some 50-fold less than in the Drosophila material. 
We feel it highly probably that this will be a general observation as more tissues are 
examined. 
In this paper we have confined the discussion largely to methods and a very general 
description of results. The methods are quite satisfactory as far as they go, but still 
more systems for separation will be needed to permit total analyses of the many 
components indicated by the results so far obtained. The results, themselves, demon- 
strate that there exists in Drosophila a very large and complex pool of peptides and 
amino acid derivatives which should be considered as potential substrates for synthesis 
of protein. However, it is a foregone conclusion, that the size and complexity of such 
a pool is no measure of its metabolic importance. 
The extraction method described here is highly satisfactory and it should be applic- 
able to any kind of biological material. The separation of substances by solubility is 
remarkably clear cut (Fractions 1 and 3 especially) and with the Drosophila material 
few if any substances appear in more than one fraction in significant quantities. 
This, of course, is not necessarily true for all materials and each system will require 
separate consideration. It should also be emphasized that, although low-molecular 
weight peptides predominate in Fraction 1 and larger ones in Fraction 3, this will 
always be influenced by composition. 
References p. 146 
