Biosynthesis of the pyrimidinyl amino acid lathyrine by Lathyrus tingitanus L.

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.

Metabolism of Pyrimidines and Purines

“…LAMBEIN et al 1976) and other legumes (KRAUSS and REINBOTHE 1973). Biosynthesis of lathyrine, willardiine, and isowillardiine were discussed in terms of two independent routes: (1) Their formation from a preformed heterocyclic compound such as uracil; (2) The cyclization of y-hydroxyhomoarginine (ASHWORTH et al 1972, BROWN andAL-BALDAWI 1977). More recently, willardiine and isowillardiine have been synthesized in vitro by use of uracil, O-acetyl-L-serine, and an enzyme extract from Pisum and other sources, this evidence favoring the former pathway (MURAKOSHI et al 1978).…”

Non-Protein Amino Acids: A Review of the Biosynthesis and Taxonomic Significance

“…Homoarginine (48) is not the most important precursor of lathyrine in L. tingitanus, however. It was shown [34,35] that "uracil (35) supplies a preformed pyrimidine ring for lathyrine biosynthesis, and that serine donates an intact 3-C unit to form the alanine side chain". They also showed that the incorporation of radioactivity from [guanidino-14 C]homoarginine into lathyrine was less than 4% of that incorporated from a similar amount of [2-14 C]uracil of comparable specific activity.…”

“…This pyrimidine amino acid (47) differs from willardiine (33) and isowillardiine (34) in having the alanine side chain attached to a ring carbon rather than a ring nitrogen. The co-occurrence in lathyrinecontaining species [30] of homoarginine ( 48) and 4-hydroxyhomoarginine ( 49) lent support to an earlier suggestion [31] that lathyrine might be formed from homoarginine in a series of steps involving hydroxylation and acclimation.…”

A New Guanidine Alkaloid from Millettia laurentii

“…These compounds, along with millettonine (4), are the first alkaloids characterized from Millettia species, and have a new type of three-ring skeleton with a guanidine and a terpenic moiety. From a biosynthetic point-of-view it is clear that a part of the cyclohexanediol unit has an isoprenoid origin, and the pyrimidine moiety may arise from the ororate pathway as postulated for the unusual amino acid lathyrine (5,6).…”