LATHYRINE BIOSYNTHESIS AND THE ORIGIN OF THE PRECURSOR 2-AMINO-4-CARBOXYPYRIMIDINE IN LATHYRUS-TINGITANUS

The biosynthetic route from uracil (2,4-dihydroxypyrimidine) to lathyr ine was examined to see if during the production of 2-amino-4-carboxyp yrimidine, the immediate precursor of lathyrine, 2-amination precedes or follows 4-carboxylation. Initially, the effect of the presence of a relatively large pool of each of the possible intermediates on the in corporation of [2-C-14]uracil into lathyrine by excised shoots of seed lings of Lathyrus tingitanus was investigated. Whereas 2-amino-4-hydro xypyrimidine (isocytosine) had no significant effect, the presence of a pool of 2-hydroxy-4-carboxypyrimidine diluted the specific activity of the radioactive lathyrine synthesized to 67% of the control value w ithout inhibiting lathyrine synthesis. In the same experiment, 2-amino -4-carboxypyrimidine, the known immediate precursor of lathyrine, decr eased the specific activity to 46% of the control value without inhibi ting lathyrine synthesis. In a subsequent experiment using an enzymic extract of L. tingitanus seedlings, [2-C-14]uracil was shown to be inc orporated into 2-hydroxy-4-carboxypyrimidine, 2-amino-4-carboxypyrimid ine and lathyrine. The data indicate that 2-hydroxy-4-carboxypyrimidin e is an intermediate in lathyrine biosynthesis and that carboxylation precedes amination in the production of the lathyrine precursor 2-amin o-4-carboxypyrimidine. Copyright (C) 1996 Elsevier Science Ltd