INVITED DISCUSSION 
TEE USE OF “C-LABELED COMPOUNDS IN METABOLIC STUDIES: 
EREECDIS DUE LO AULOCEAVING “C_UREA 
Jin KO BPOLEARD? 
Department of Botany, Cornell University, Ithaca, N.Y. (U.S.A.) 
In the course of certain studies on the metabolism of urea (LYNDON, POLLARD AND 
STEWARD!), urea seemed to form a compound toxic to carrot tissue cultures on auto- 
claving. To help characterize the change in urea on autoclaving, samples of “#C-urea 
were autoclaved in the medium used to grow the carrot tissue cultures, and then 
analyzed by paper chromatography and radioautography with the results shown 
in Fig. 1. 
Apparently, urea at least, forms a bewildering array of unidentified products when 
it is autoclaved in a somewhat complex medium. While none of the compounds so 
produced have been specifically identified, this note merely emphasizes the range of 
substances easily formed from a compound as simple as urea when it is autoclaved. 
There are two implications in these results. The first is that compounds produced by 
autoclaving could be mistakenly attributed to metabolic transformations of the 

ry A 
aS PHENOM) . Sota 
Fig. 1 A + B. Radioautographs of the chromatograms of (A) “C-urea and (B) of C-urea auto- 
claved in modified White’s medium containing 10° coconut milk. 



* Present address: Calbiochem, 3625 Medford St., Los Angeles 63, Calif., U.S.A. 
Reference p. 70 
