Toxicology and metabolism of L-canavanine in the tobacco budworm, Heliothis virescens (Noctuidae);

scL-Canavanine, the toxic guanidinooxy structural analog of scL-arginine found in many leguminous plants, was fed to larvae of the tobacco budworm, Heliothis virescens (Noctuidae). Canavanine-feeding studies revealed that H. virescens larvae were resistant to the potentially insecticidal effects of this protective allelochemical and established an {dollar}rm LCsb{lcub}50{rcub}{dollar} in the terminal instar larvae of 300 mM. The {dollar}rm LDsb{lcub}50{rcub}{dollar} in the terminal instar larvae was 10.6 g/kg. Injected canavanine was cleared from the hemolymph with a {dollar}rm tsb{lcub}1/2{rcub}{dollar} of 135 min. Feeding studies employing other nonprotein amino acids revealed that this destructive generalist feeder could not cope with all toxic nonprotein amino acids. Neither larval maintenance on a diet of 150 mM scL-canavanine for 48 hr nor cycloheximide-mediated inhibition of larval protein synthesis affected the larval clearance rate for canavanine. Moreover, the electrophoretic profile of larval hemolymph, gut and fat body proteins in insects maintained on 150 mM dietary canavanine for 72 hr or provided 5 g/kg canavanine by injection were unaltered relative to control larvae.; Heliothis virescens, a canavanine resistant insect, failed to accumulate significant canavanyl proteins. This finding supported the contention that the incorporation of canavanine into proteins in place of arginine contributes to canavanine's antimetabolic properties.; Heliothis virescens larvae, administered 5 g/kg scL-canavanine supplemented with 37.7 KBq scL- (guanidinooxy-{dollar}rm sp{lcub}14{rcub}C{dollar}) canavanine, were sacrificed from 0 to 12 hr post-injection. Twelve hours after treatment, 8.6% of the administered ({dollar}rm sp{lcub}14{rcub}C{dollar}) canavanine was unmetabolized. Analysis of the 12 hr samples revealed the principal products of scL-canavanine degradation were ({dollar}rm sp{lcub}14{rcub}C{dollar}) guanidine and ({dollar}rm sp{lcub}14{rcub}C{dollar}) urea; these metabolites accounted for 72.3% and 8.7%, respectively of the administered ({dollar}rm sp{lcub}14{rcub}C{dollar}) carbon. scL-(1,2,3,4-{dollar}rm sp{lcub}14{rcub}C{dollar}) Canavanine and scL- (U-{dollar}rm sp{lcub}14{rcub}C{dollar}) canaline were synthesized to study the metabolic fate of the aliphatic portion of canavanine and canaline. scL- (1,2,3,4-{dollar}rm sp{lcub}14{rcub}C{dollar}) canavanine was metabolized to ({dollar}rm sp{lcub}14{rcub}C{dollar}) homoserine, ({dollar}rm sp{lcub}14{rcub}C{dollar}) aspartate/asparagine, ({dollar}rm sp{lcub}14{rcub}C{dollar}) glutamate/glutamine, ({dollar}rm sp{lcub}14{rcub}C{dollar}) 2-aminobutyrate, ({dollar}rm sp{lcub}14{rcub}C{dollar}) ornithine, ({dollar}rm sp{lcub}14{rcub}C{dollar}) proline, ({dollar}rm sp{lcub}14{rcub}C{dollar}) isoleucine and ({dollar}rm sp{lcub}14{rcub}C{dollar}) {dollar}rm COsb2{dollar}. scL- (U-{dollar}rm sp{lcub}14{rcub}C{dollar}) canaline was metabolized to ({dollar}rm sp{lcub}14{rcub}C{dollar}) homoserine, ({dollar}rm sp{lcub}14{rcub}C{dollar}) glutamate/glutamine, ({dollar}rm sp{lcub}14{rcub}C{dollar}) aspartate/asparagine, ({dollar}rm sp{lcub}14{rcub}C{dollar}) 2-aminobutyrate and very little {dollar}rm COsb2{dollar}.