FREE AMINO ACIDS IN INSECTS 129 
Bai reported that the predominant proteins in the insect studied by them probably 
belong to the albumin group. As a matter of fact, we do not yet know much about the 
nature of blood proteins in insects. Their electrophoretic patterns are species- 
specific*®. 17°, and it is certainly over-simplified to classify them just as albumin or 
globulin. 
According to CHEN: 3° in both Drosophila and Culex larvae there is a rapid in- 
crease in the contents of blood proteins, especially towards the end of larval develop- 
ment. A similar increase has been reported for Bombyx mori”: 1% and Galleria mello- 
nella*®. Using labelled glycine BrIcTEUX-GREGORIE ef al.2® demonstrated that in 
Sphinx ligustri the adult proteins are synthesized directly from free amino acids. This 
fact points out that the decrease of free amino acids during development is largely 
due to their incorporation into the proteins. In the mealworm Tenebrio molitor, Po- 
CHEDLEY"! observed that the contents of soluble proteins show characteristic changes 
at various developmental stages. Similar results have been also reported by HELLER” 
for Deilephila euphorbiae and by Lupwic?” for Popillia japonica. Parallel to protein 
synthesis, variations in RNA contents of Tenebrio during morphogenetic development 
have been detected”. 
EFFECTS OF GENES ON FREE AMINO ACIDS 
The genic control of protein metabolism has been repeatedly demonstrated by genetica] 
and biochemical studies on both microorganisms!** and higher animals?. In insects, 
examples are known which show that mutational effects influence to various extents 
the free amino acid pool.We need only to mention the accumulation of free tryptophane 
in the v-mutant of Drosophila melanogaster®? and in the a-mutant of Ephestia kiih- 
niella!, 68, In both cases, the oxidation of tryptophan to kynurenine does not take 
place. More drastic changes have been reported from studies on lethal factors. This 
problem has been treated in detail by HADRON*: 89. 
NAKAMURA ef al.‘ found in D. melanogaster the presence of one substance, probably 
cystine, in the lethal embryos, but not in normal ones. Their further studies on 
two embryonic lethal factors revealed that the amounts of glutamic acid, aspartic 
acid, glycine, arginine, threonine and serine show a larger decrease in the lethals, 
but apparently less in the controls. 
From his studies on a melanoma-producing lethal in Drosophila, LEwis!”* reported 
that the tumor larvae have no cystine. They have, however, a higher concentration 
of alanine, arginine, glycine, methionine, serine and tyrosine. The concentration of 
methionine and tyrosine was found to be lower in the heterozygotes. 
More detailed studies on the protein metabolism of two lethal factors, “Jethal- 
translucida” (ltr) and “lethal-meander” (lme), of D. melanogaster have been under- 
taken by Haporn and his collaborators**. The /tv-homozygotes accumulate a large 
amount of hemolymph and stop development in the pupal stage’’. Biochemical 
analyses showed that the concentration of free amino acids is much higher in these 
lethal individuals than in the corresponding normals”: *'. The increase, however, is not 
the same in different amino acids!*. Since the /tv-homozygous larvae have a very low 
content of blood proteins, it seems that the process of protein synthesis in this mutant 
is 1nhibrted: tone = 
The /me/lme larvae stop development in the third instar and never pupate’®. 
References p. 132/135 
