UNUSUALLY HIGH-CONCENTRATION OF FREE GLYCINE IN THE MIDGUT CONTENT OFTHE SILKWORM, BOMBYX-MORI, AND OTHER LEPIDOPTERAN LARVAE

In the course of investigating the digestion and the absorption of die tary protein by the silkworm, Bombyx mori, reared on an artificial die t, we found the existence of an unusually high concentration of free g lycine in the midgut content compared with other amino acids. To test whether this free glycine is from diet or from the silkworm itself, si lkworm larvae were fed a diet without a protein source for 1 day and t he free amino acids in the midgut content were then analyzed. Unexpect edly, the concentration of free glycine in the midgut content was stil l high (8.98 mu moles/g midgut content). In contrast, the concentratio ns of other amino acids were very low, and none of them exceeded 1/20 that of glycine. The concentration of free glycine was high in the ant erior half of the midgut, and it decreased toward the posterior region . Free glycine was virtually undetected in the feces. To examine if th is phenomenon has ally generality, the same experiments were repeated with the sweet potato hornworm, Agrius convolvuli, and the rice armywo rm, Pseudaletia separata. A phenomenon similar to that in the silkworm was observed in Agrius convolvuli, but in Pseudaletia separata, no am ino acid, including glycine, had a high concentration. We also found t hat an unusually high concentration of free glycine exists in the dige stive juice of Bombyx mori. These results suggest that free glycine is secreted into the intestinal lumen and that the free glycine might ha ve some unknown biological role.