748 B. AXELROD, J. L. HAINING, T. FUKUI 
phospholipids, the quantity of which decreases sharply when protein synthesis begins. 
The investigations of HENDLER on oviduct mince have provided stronger insinuations. 
These investigations have been thoroughly pursued and extended to other orga- 
nisms! 1, Fortunately HENDLER is present so we can look forward to an authorita- 
tive presentation and a critical evaluation of the issue. 
Strong claims for the participation of lipo—amino acid complexes in protein syn- 
thesis have been put forth by HUNTER AND GooDALL!’. These workers following up 
an earlier lead which HUNTER e¢ al.4 obtained in studying the incorporation of amino 
acids into cytoplasmic membranes of Bacillus megaterium, fed C-labeled amino 
acids to protoplasts. They isolated therefrom lipo—amino acid complexes which were 
composed of both phospholipid and non-phospholipid fractions. Incubating in the 
presence of chloramphenicol or crotoxin prevented their formation. A number of 
amino acids were suitable for the purpose of preparing radioactive lipo—amino acid 
complexes. Strangely enough, phenylalanine behaved in an aberrant manner. A 
complex prepared with radioactive threonine was isolated and incubated with proto- 
plasts. In 30 min over 70% of the activity appeared in the protein. If a great excess 
of unlabeled threonine was added there was no diminution in the amount of activity 
taken up. It was therefore claimed that the amino acid of the complex can be taken 
directly into protein without prior conversion to free amino acid. However, radio- 
active threonine itself was readily incorporated into protein and lipid. If the quantity 
of unlabeled threonine used in the above experiment was of an order of magnitude 
required to saturate the system (and this would have to be the case for the con- 
clusion to be valid) then it would be necessary to argue that the lipo-threonine com- 
plex or the olive oil used as its vehicle, suppressed the normal incorporation, or that 
there are a tremendous number of sites for deposition of the amino acid. 
In our studies we have found that dilution of radioactive phenylalanine with un- 
labeled amino acid reduced incorporation into protein, but had no effect on the lipo— 
amino acid. The amino acid-activating enzymes are characterized by low K, values, 
while the lipo—amino acid forming system we found, is not saturated by high con- 
centrations of phenylalanine. 
GABY et al.!° have obtained phospholipid—amino acid complexes from Penicillium 
chrysogenum. Using radioactive amino acids they have concluded that amino acids 
are taken up at a faster rate by the phospholipids than by the water-soluble amino 
acid pool. While they have expressed no conclusions concerning the role of the lipo— 
amino acid complex in protein synthesis they indicate that they have an active role 
in the utilization of amino acids. 
We are indebted to LEDERER for drawing our attention to the existence of a natu- 
rally occurring fatty acid—amino acid combination, found in some species of Myco- 
bactertum'®, Thus one obtained from M. marinum? and another from M. avium!® 
contain together with three unusual deoxy sugars, a pentapeptide, whose N-terminal 
amino acid is attached to a long chain carboxylic acid. 
sacteria are fruitful sources of strange compounds. Thus B. civculans provides in 
the antibiotic circulin another example of a peptido—-acyl combination. Here tL-a, y- 
diaminobutyric acid is attached via its y-amino group to 6-methyloctanoic acid’. 
MAALGE has pointed out that if lipo—amino acids can serve as a sort of transient 
storage site for amino acids they cannot be ignored in estimating the amino acid 
pool size when studying enzyme induction and repression in the cell. 
References p. 749 
