METABOLIC FLUX AND INCORPORATION OF [2-C-13]GLYCINE INTO SILK FIBROIN STUDIED BY C-13 NMR INVIVO AND INVITRO

C-13 NMR spectra in vivo and in vitro of Bombyx mori silkworm larva and the posterior silk gland were observed after administration of [2-C-13]glycine. In the in vivo C-13 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-C-13]glycine flux was analyzed with eight rate constants which were determined with a compartment model. The incorporation of [2-C-13]glycine into the silk fibroin was also observed by C-13 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 x 10(-4) min-1. This was 63% of the rate constant determined in vivo.