We found that a considerable amount of free glycine exists in the digestive juice of several leaf-feeding Lepidopteran larvae.
Evidence suggests that the glycine is secreted by larvae into gut lumen.
The concentration of glycine has very clear correlation with the protein denaturing activity of the host plant. We found that the leaf extract of the privet tree, Ligustrum obtusifolium , has extremely strong protein denaturing activity enough to make a protein innutritive. The denaturing activity closely resembles those of polyphenolics, general defense agents widespread throughout plants including leaves of the privet tree. The species which feed on this host plant have an extremely large amount of glycine in their digestive juice. We demonstrate that free glycine can completely inhibit the denaturing activity of the privet leaf in vitro, and that free glycine can prevent the protein from becoming innutritive using bioassay.