Metabolism of L-canavanine and L-canaline in the tobacco budworm, Heliothis virescens [Noctuidae]

Abstract

The metabolism of L-canavanine and L-canaline were investigated in larvae of the tobacco budworm, Heliothis virescens [Noctuidae]. H. virescens larvae were treated with L-[1,2,3,4-14C]canavanine or L-[U-14C]canaline with sufficient cold carrier to provide 5 mg g-1 canavanine or a molar equivalent of canaline (3.81 mg g-1). The preponderant catabolite in both canavanine- and canaline-treated larvae was [14C]homoserine. Other minor metabolites derived from canavanine included [14C]aspartate/asparagine, [14C]glutamate/glutamine, [14C]2-aminobutyrate, [14C]ornithine, [14C]proline, and [14C]isoleucine. Canaline yielded [14C]glutamate/glutamine, [14C]aspartate/asparagine, and [14C]-2-aminobutyrate. Our current studies support the belief that this destructive insect tolerates L-canavanine and L-canaline because of its ability to reductively cleave these potentially insecticidal natural products to L-homoserine and guanidine or ammonia, respectively.

The biochemical basis for l -canavanine tolerance by the tobacco budworm Heliothis virescens (Noctuidae)

“…In contrast, tobacco hornworm larvae, Manduca sexta, maintained on a 2.5 mM canavanine-containing diet develop massive developmental aberrations (1,2). The appreciable natural resistance of H. virescens to this protective allelochemical instigated earlier studies to elucidate the biochemical basis for canavanine tolerance by H. virescens (7)(8)(9).…”

“…Administration of L-[guanidinooxy- 14 C]canavanine to fifth instar H. virescens larvae disclosed that [ 14 C]guanidine was the principal in vivo larval radiolabeled canavanine catabolite (9). Subsequent in vivo studies employing L- [1,2,3,4-14 C]canavanine identified L- [1,2,3,4-14 C]homoserine as the preponderant radiolabeled catabolite (9). These studies of radiolabeled metabolite disposition implicated a larval reductase in the detoxification of canavanine via homoserine and guanidine.…”