OCCURRENCE OF FREE AMINO ACIDS — INSECTS 147 
METABOLISM OF PEPTIDES IN DROSOPHILA 
JOHN R. SIMMONS anp HERSCHEL K. MITCHELL 
California Institute of Technology, Division of Biology, Pasadena, Calif. (U.S.A.) 
As reported in the previous paper!, Drosophila larvae contain a wide variety of amino 
acid derivatives, many of them being peptides. This pool of materials is a very large 
and complex one and many components are present in relatively high concentrations. 
This system therefore appears to be a very good one for studies on the synthesis and 
metabolism of peptides and related substances. A good deal of work in this direction 
has been done? using [!4C] amino acids and a summary of results obtained so far is 
given in this report. 
METHODS 
Most of the methods used here have been described in the previous paper’. Injections 
of Drosophila larvae were carried out using an apparatus developed for the purpose 
(H. K. MitcHELt, unpublished) and by its use we were able to inject large numbers 
of larvae with a volume of as little as 0.05 wl with an error of approx. + 25%. This 
was determined by direct counts of squashed single larvae injected with [@C} glutamic 
acid. The error is considerably less in adults or in water drops where there is little 
or no back pressure. For studies of incorporation of amino acids in time series, larvae 
were injected and washed thoroughly with water. They were then placed on washed 
filter paper and squashed with a glass rod as described earlier’. Unless otherwise 
indicated, the solvent used for chromatography was -propanol-I% aqueous am- 
monia (3 : 1). Radioactive areas on paper chromatograms were determined by use of 
a paper strip counter (Nuclear Chicago) and a planimeter. Results are reported as 
percentage of the total radioactivity injected for each sample and the corresponding 
strip. 
RESULTS 
Glutamic acid incorporation in direct squash experiments. The results recorded in Table I 
and Fig. 1 are typical of the pattern found in seven different series in which glutamic 
acid was injected into third-instar larvae. At the earliest time intervals the major 
radioactive peak matched the chromatographic position of known glutamic acid 
very closely. With increasing time from injection there was a marked tendency for 
this area of greatest radioactivity to shift to higher Ry. When the area was eluted, 
hydrolyzed and rechromatographed it once more closely matched known glutamic 
acid in position. It would thus seem that the major chromatographic peak is multi- 
component in nature, and that the proportion of the various components change with 
time. All of the radioactive areas showed corresponding ninhydrin-positive reactions, 
but since the ninhydrin pattern from whole animals is very complex it would be a 
References p. 155 
