Lathyrine biosynthesis and the origin of the precursor 2-amino-4-carboxypyrimidine in Lathyrus tingitanus

Abstract

Abstract The biosynthetic route from uracil (2,4-dihydroxypyrimidine) to lathyrine was examined to see if during the production of 2-amino-4-carboxypyrimidine, 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 incorporation of [2- 14 C]uracil into lathyrine by excised shoots of seedlings of Lathyrus tingitanus was investigated. Whereas 2-amino-4-hydroxypyrimidine (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 without inhibiting lathyrine synthesis. In the same experiment, 2-amino-4-carboxypyrimidine, the known immediate precursor of lathyrine, decreased the specific activity to 46% of the control value without inhibiting lathyrine synthesis. In a subsequent experiment using an enzymic extract of L. tingitanus seedlings, [2- 14 C]uracil was shown to be incorporated into 2-hydroxy-4-carboxypyrimidine, 2-amino-4-carboxypyrimidine and lathyrine. The data indicate that 2-hydroxy-4-carboxypyrimidine is an intermediate in lathyrine biosynthesis and that carboxylation precedes amination in the production of the lathyrine precursor 2-amino-4-carboxypyrimidine.