752 R. W. HENDLER 
lipid complexes to an extent approx. 1o-fold greater than the other amino acids?: 9. 
HAINING ef al. also found that phenylalanine and tryptophane were similarly of a 
different order of magnitude in their ability to label lipid complexes when compared 
to other amino acids. In their metabolic studies, they isolated the total lipid fraction 
after hot trichloroacetic acid treatment. By so doing, they may have destroyed 
certain amino acid complexes not able to stand these conditions. In one of their 
studies, AXELROD et al. found that by adding unlabeled phenylalanine to a small 
amount of labeled phenylalanine the total radioactivity of the lipids did not decrease, 
whereas the radioactivity of the protein was decreased. Since we have shown that 
the lipid sites are far from saturation while the protein-forming system is near 
saturation, such experiments are not inconsistent with the amino acid passing 
through the lipid en route to the protein. 
The existence of an enzyme for catalyzing the formation of N-fatty acylphenyl- 
alanine was well established, as well as various properties of the enzyme, and it will 
be worthwhile to investigate the possible metabolic significance of this new finding. 
However, I think it important to emphasize that these studies cannot be inter- 
preted at present in terms of the relation of amino acid—lipid complexes to protein 
synthesis. 
Hunter et al. have recently become very much interested in the possible role of 
lipids in protein synthesis in b. megatertum*. They have been able to repeat in their 
system many of the characteristics reported for the hen oviduct system such as: the 
ability of many amino acids to form such complexes; the relatively rapid kinetics 
for amino acid labeling of the lipid complexes compared to the labeling of the ribo- 
nucleic acid and protein; the unusual nature of lipid complexes formed from phenyl- 
alanine; the fact that lipid—amino acid complexes containing little or no phosphorus 
could be obtained; and that the amino acid incorporation process is quite sensitive 
to lecithinase A. In addition, they have reported that radioactivity could be trans- 
ferred from an isolated lipid—amino acid complex to the protein of their membrane 
fraction and that the incorporation of amino acid into the lipid complexes is inhibited 
by chloramphenicol. 
Gaby et al. have been concerned with the possible involvement of phospholipid 
in the transport of amino acid across cell walls! 1*. They have observed that amino 
acid becomes firmly bound to phospholipid upon incubation with the metabolizing 
cells. Furthermore, the amino acid is held in the phospholipid in a metabolically 
exchangeable form as opposed to being held in the form of stable end-product. Similar 
evidence for the involvement of phospholipid in the metabolism of amino acid was 
obtained with cells of Penicillium chrysogenum, rabbit liver, rabbit lymph node and 
Ehrlich ascites tumor. Similar findings were made for several of the amino acids. 
These studies are clear in their implication and are being pursued further. It is to be 
hoped that the examination will be extended to the less polar lipids. 
WerstLEY, WREN AND MITCHELL have found several chromatographically different 
amino acid—lipid complexes in Drosophila melanogaster, whole human blood and other 
sources! }8, 14, During maturation of the Drosophila larvae, a major quantity of 
amino acid appears to move from a lipid-soluble form eventually into newly formed 
protein. These authors provide an excellent review of papers since the early 50’s 
reporting the presence of amino acid in lipid fractions. The question of artefacts has 
been seriously considered in these works and various procedural operations are 
References p. 758 
