Metabolic flux and incorporation of [2-13C]glycine into silk fibroin studied by 13C NMR in vivo and in vitro

Abstract 13 C NMR spectra in vivo and in vitro of Bombyx mori silkworm larva and the posterior silk gland were observed after administration of [2- 13 C]glycine. In the in vivo 13 C NMR spectra of larva, the administrated glycine flowed immediately from the midgut to the hemolymph and was then incorporated into the silk fibroin. This [2- 13 C]glycine flux was analyzed with eight rate constants which were determined with a compartment model. The incorporation of [2- 13 C]glycine into the silk fibroin was also observed by 13 C NMR spectroscopy by circumfusion cultivation of the posterior silk gland. The rate constant for the incorporation of glycine in vitro was determined as 7.4 × 10 −4 min −1 . This was 63% of the rate constant determined in vivo .