SEP AND LOMBRICINE 189 
both p- and 1L-{8H]serine into D-SEP and p-lombricine was taken?® as indicating a 
change from the L- to the D-isomer, although it was not possible to determine whether 
this change took place before, or at the moment of incorporation. Administration 
of pi-[3-M@C|serine resulted in radioactivity appearing in both the guanidinoethanol 
and serine parts of the molecule, as would be expected if a decarboxylation of serine 
took place!®. 
The presence of D-serine in SEP and lombricine isolated from earthworms and the 
incorporation of isotopically labeled b-serine into both of these compounds suggested 
the possible presence of D-serine in the free amino acid pool of the earthworm. b-serine 
has been isolated!’ from perchloric acid extracts of earthworms and in a more detailed 
investigation!® unequivocal evidence was adduced to show that the pD-isomer could 
not have arisen as a result of racemization induced by the techniques and solutions 
used in the isolation procedure. There can be no doubt, therefore, that in the earth- 
worm D-serine has a biological origin, although the precise nature of this origin is a 
matter for conjecture. It has been reported® that lombricine undergoes enzymatic 
degradation and although no evidence was adduced to support this contention, it 
would provide a possible explanation for the presence of free D-serine in the free amino 
acid pool. However, experiments!® by the present authors have failed to confirm the 
reported lability of lombricine in earthworm homogenates. Experiments designed to 
give a definitive answer to the question of the origin of D-serine in the earthworm 
are In progress. 
The importance of lombricine in the earthworm lies in the fact that it is the guanidino 
base of the phosphagen, N-phosphoryllombricine (PL). PL was first isolated from 
earthworms as an impure compound by TuHoat et al.!®, 2° but has since been obtained 
in good yield from natural sources as chemically pure barium, magnesium and am- 
monium salts*!. The isolation method involves the use of ion-exchange techniques 
and gives practically quantitative recoveries. 
N-phosphoryllombricine of the structure { , 
(/ 
NH-PO,-H, * 
HN-=C O Vy 
\ | | “uO! 
IN; CHE-CE5-O:P-©-CH,-CH-COOEH \ 
H | | 
OH NH, 
has been synthesized** and shown to be identical with the naturally occurring com- 
pound?s. Proof that this compound acts as a phosphagen has been afforded by the 
demonstration™ of an enzyme which catalyzed the reaction: 
Lombricine + ATP = PL + ADP 
The enzyme was activated by Mg?+, Co*+ and Mn?+, but not by Ca?+ or Sr?+, and 
catalysed the phosphorylation of both the naturally-occurring p-lombricine and the 
synthetic L-isomer. The preparation examined also catalysed the phosphorylation of 
taurocyamine but whether this was due to a lack of specificity or to possible contamina- 
tion with taurocyamine phosphoryltransferase (TPT) is not known with certainty. 
Somewhat similar observations have been made by PANntT?®, who used extracts of 
References p. 192/193 
