FREE AMINO ACIDS IN INVERTEBRATES 169 
fb-Aminoisobutyric acid 
f-Aminoisobutyric acid was identified in extracts from Mytilus edulis by AWAPARA 
AND ALLEN*® and in a number of flatworms by CAMPBELL*®®. The same flatworms 
contained f-alanine indicating that the two f-amino acids were formed probably 
from pyrimidines as in the mammal?? #9. CAMPBELL” investigated pyrimidine meta- 
H,C—NH, 
| 
H,C—C—H 
| 
COOH 
bolism in the parasitic flatworms Hymenolepsts diminuta and showed that uracil and 
thymine are degraded to f-alanine and f-aminoisobutyric acid respectively. The 
degradation of {2-!4Cjuracil resulted in the formation of radioactive dihydrouracil, 
carbamyl-/-alanine, carbon dioxide and in addition a/ 1-'C|alanine, some unidentified 
compounds and an organic acid which was tentatively identified as succinic acid. The 
presence of /-aminoisobutyric acid in the clam M. edulis also indicates that pyrimi- 
dines could break down in marine invertebrates by a similar route. Evidence for this 
has been obtained in our laboratory by CAMBPELL AND ALLEN. They showed formation 
of B-alanine in Rangia cuneata after injection of uracil, carbamyl-f-alanine and dihy- 
drouracil. 
Lombricine 
The isolation of lombricine from the earthworm Lumbricus terrestris was first des- 
cribed by VAN THOAT AND Ropin®!. ROSENBERG AND ENNOR®*® described a simple 
method to isolate lombricine; they also found that the earthworm contained a phos- 
phodiester of serine and ethanolamine; this phosphodiester (2-aminoethyl-2-amino- 
O 
I| 
HN—CH,—CH,—O—P—O—CH,—CH—COOH 
| | | 
H,N—C = NH OH NH, 

2-carboxyethyl hydrogen phosphate) was postulated as a precursor of lombricine. 
Such a phosphate ester was not new in the animal kingdom for RoBERTS AND LOWE*? 
had already found it in the muscle of turtles. The serine in the ester from turtles was 
reported to be L-serine whereas in lombricine serine exists as the D-enantiomorph*. 
More work by EnNor et al. permitted them to isolate a sufficient quantity of the phos- 
phodiester of serine and ethanolamine to identify it by chemical and physical means. 
The serine portion of the molecule was D-serine. This fact provided sufficient evidence 
to favor its precursor role in the formation of lombricine. 
The biosynthesis of lombricine was finally demonstrated by RossITER, GAFFNEY, 
ROSENBERG AND ENNoR®*. Labeled precursors were administered to earthworms 
(Megascolides cameroni): *2P;, [1 : 2-4C]ethanolamine, [3-!4C]serine and _ L-{“C)- 
amidinoarginine. Lombricine was obtained by chromatography on filter paper and 
radioactivity determined; the serine ethanolamine phosphodiester was also separated 
References p. 174/175 
