| Abstract: | The biosynthesis of the pyrimidinyl amino acid lathyrine by seedlings of Lathyrus tingitanus L. was shown to be stimulated by uracil. 6(-14)C]Orotate, 2(-14)C]uracil and 3(-14)C]serine were incorporated into lathyrine; the incorporation of 6(-14)C]orotate was substantially decreased in the presence of uracil. Chemical degradation to locate the 14C incorporated from labelled precursors showed that 90% of the radioactivity incorporated into lathyrine from 3(-14)C]serine could be recovered in the alanine side chain. Over 80% of the radioactivity incorporated from 2(-14)C]uracil was shown to be located in C-2 of lathyrine. It is concluded that under the conditions studied, lathyrine arises from a preformed pyrimidine arising via the orotate pathway. Paradoxically, it was also possible to confirm previous reports that radioactivity from L-guanidino-14C]homoarginine is incorporated into lathyrine and gamma-hydroxyhomoarginine. However, as homoarginine and gamma-hydroxyhomoarginine are also both labelled by 2(-14)C]uracil, it is suggested that they are products of the ring-opening of lathyrine and that reversibility of this process accounts, at least in part, for their observed experimental incorporation into lathyrine. |
