130 P. S. CHEN 
Paper chromatographic analyses revealed that in the aged lethal homozygotes the 
essential amino acids are either entirely absent (valine, leucine, isoleucine, methionine, 
histidine, arginine, lysine) or greatly reduced (threonine). On the other hand, they 
accumulate an abnormally high concentration of glycine, especially in later stages’. 
Experiments 77 vitro suggest that a much reduced activity of proteolytic enzymes in 
the gut is probably responsible for the abnormal protein metabolism in this mutant 
(for peptides in these two lethal mutants, see paper by MITCHELL AND SIMMONS in 
this conference). 
Recently, chromatographic analyses on three more lethal factors in Drosophila 
have been carried out in HAporn’s laboratory. For the factor “Jethal-bluter” (lbl) 
BENz”° observed that the homozygous /b/-individuals in the third larval instar have 
distinctly less free amino acids than the normal ones. Since the lethals have a thicker 
cuticle, it is possible that a larger amount of these substances are used for the syn- 
thesis of cuticular proteins. For the factor “lethal-polymorph” (lpm) it was found that 
in the larval stage the /pm-lethals have an abnormally high concentration of free 
ninhydrin-reacting components, although the difference becomes less distinct in the 
prepupal stage. According to BENz” this is probably related to the abnormal formation 
of muscular proteins in the /pm-homozygotes. In a recent paper FAULHABER® pre- 
sented data on the protein metabolism of the mutant “Jethal giant larvae” (igl). Her 
results indicate that in the /g/-lethals there is an excess of free amino acids and a 
deficiency of blood proteins. The situation is therefore very similar to that found for the 
factor “lethal-translucida”’, apparently also due to a reduced protein synthesis. 
From all studies just cited, it is evident that the lethal factors have a distinctly 
specific effect on protein metabolism. Each lethal-mutant has its own free amino 
acid pattern. As suggested by the work of CHEN?® and BENz”®, the targets of the lethal 
effects vary from case to case; protein formation either in blood, muscle or cuticule is 
impaired. In the case of lethal-meander it seems that mainly the proteolytic enzymes 
are affected*®. These facts imply that specific genes are involved in these mutants. 
However, until more information is available, we do not know whether the observed 
abnormal protein metabolism results from a direct or indirect effect of the mutational 
process. 
SPECIAL FUNCTIONS AND METABOLIC INTERRELATIONSHIPS OF FREE AMINO ACIDS 
In the previous section the developmental roles of amino acids have been mentioned 
(p. 124). In the following, we shall consider some other specific functions of these 
substances. The free amino acids are believed to play an active part in adjusting the 
osmotic pressure and the buffering action of the body fluid®: 187, 27, 198, 86. The work 
of DucHATEAU AND FLORKIN®’ showed that in the marine crustaceans dilution of 
sea water resulted in a decrease of the amino acid concentration. On the other hand, 
the fresh-water form, after being transferred into the sea water, showed an increase 
in the concentration of amino acids, especially that of proline. However, glycine seems 
to be also effective in osmoregulation?®, 1°, 32, It is known that glycine participates 
in many activities of the cell!®*, The growth-promoting effect of glycine in Drosophila 
development has been referred to in a previous section (p. 127). 
Various studies demonstrated that dietary amino acids have a distinct effect on 
egg production in insects. Thus, GREENBERG* observed that oviposition in Aedes 
References p. 132/135 
