SEP AND LOMBRICINE IQ! 
The high concentration of SEP in the small intestine compared with that in other 
tissues (apart from kidney) is of interest and may well provide a clue to the functional 
significance of this compound. Thus from the structural similarity of SEP with the 
phosphatides it is a temptation to suggest that it may be concerned with absorption 
phenomena. The results do not exclude the possibility of SEP biosynthesis in the 
small intestine but im vityo experiments with avian intestinal mucosa have failed to 
show any incorporation of *?P; into SEP under conditions which have been successful 
with avian kidney homogenates. 
Thus incorporation of =8P; has been achieved with chicken-kidney homogenates 
TABLE II 
In vityo INCORPORATION OF aes INTO SEP IN CHICKEN-KIDNEY HOMOGENATE 
Incubation mixtures contained: Mg?+, too “moles; ethanolamine, 50 sumoles; serine, 50 zmoles ; 
ADP, 50 zmoles; CTP, 5 wmoles; K-succinate, 100 zmoles; N-ethyl—-morpholine buffer (pH 7.2), 
500 ywmoles; kidney homogenate (3 g tissue) in a total vol. of 15 ml. Shaken for 2 h at 37°. 

Phosphorus SEP in mixture after 
Conditions esterified ao CERES ‘witha 
(%) pemoles counts/min eAls 
Complete mixture 4.9 0.97 779 804 
Complete mixture + DNP (3 « 10-4 M) 2.5 0.66 fe) oO 
Complete mixture less CTP — 0.92 452 491 
prepared in phosphate or N-ethylmorpholine buffer and supplemented by a number 
of possible cofactors and precursors (Table IT). 
The lack of new synthesis of SEP in the presence of dinitrophenol and its stimula- 
tion by CTP (Table IT) show that the reaction is energy-dependent and that a cytidine 
derivative may be involved in the synthesis. The nature of the reactions involved and 
the cofactors necessary are now under investigation and will be reported elsewhere. 
SUMMARY AND CONCLUSIONS 
The discovery of L- and p-SEP and of p-lombricine has revealed a number of fascinating 
problems which are gradually nearing solution. It is abundantly clear that some at 
least of the functions of the r- and p-enantiomorphs of SEP are quite different, al- 
though the possibility of the similarity of some functions cannot be discarded. Doubtless 
further work will enable this question to be resolved. 
The prime function of D-SEP is to act as a precursor of lombricine which is the guani- 
dino base of the phosphagen, N-phosphoryllombricine, in the earthworm. It is known 
that the transfer of an amidino group from arginine to an acceptor results in the for- 
mation of a compound which is metabolically inert as far as its participation in inter- 
mediary metabolism is concerned. It is tempting, therefore, although it may never- 
theless be sophistry, to suggest that p-lombricine functions not only as a phosphoryl- 
group acceptor, but also as the ultimate “sink” for the disposal of a D-amino acid the 
presence of which might conceivably lead to some derangement of normal metabolic 
mechanisms. Such a teleological explanation gains support, although not necessarily 
References p. 192/193 
