Biomedical subjects
D H Janzen
Publications and source records attributed to D H Janzen.
Degradation and detoxification of canavanine by a specialized seed predator.
Larvae of the bruchid beetle Caryedes brasiliensis feed exclusively on seeds of the Neotropical legume Dioclea megacarpa, which contains 13 percent L-canavanine by dry weight. L-Canavanine, a nonprotein amino acid analog of L-arginine, exhibits potent insecticidal properties. Most of the seed nitrogen is sequestered in canavanine, and bruchid beetle larvae do not simply excrete this toxic compound. Instead, these larvae possess extraordinarily high urease activity, which facilitates the conversion of canavanine to ammonia through urea. In this way, canavanine is effectively detoxified and a supply of nitrogen for fixation into organic linkage is ensured.
Insecticidal action of the phytohemagglutinin in black beans on a bruchid beetle.
Black bean (Phaseolus vulgaris) phytohemagglutinin added to the normal diet of a bruchid beetle (Callosobruchus maculatus) that can eat phytohemagglutinin-free cowpeas (Vigna unguiculata) but not P. vulgaris seeds kills the bruchid larvae. Trypsin inhibitors, found in both P. vulgaris and V. unguiculata seeds, have virtually no effect on the bruchid larvae. The conclusion is that a major part of the adaptive significance of phytohemagglutinins in black bean and other legume seeds is to protect them from attack by insect seed predators.
A novel means for dealing with L-canavanine, a toxic metabolite.
L-canavanine is a highly toxic L-arginine analog found in some leguminous seeds. Larvae of the bruchid beetle Caryedes brasiliensis, collected in Costa Rica, subsist solely on tissues of the mature seed of Dioclea megacarpa, which contains more than 8 percent L-canavanine by dry weight. The arginyl-tRNA synthetase of the bruchid beetle larvae discriminates between L-arginine and L-canavanine, and canavanyl proteins are not synthesized. In this way, bruchid beetle larvae avoid an adverse biochemical effect of L-canavanine.
Medical and ecological considerations of L-dopa and 5-HTP in seeds.
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