DETECTION OF CROSS-LINKS IN INSECT CUTICLE BY REDOR NMR-SPECTROSCOPY

Rotational-echo, double-resonance C-13 and N-15 NMR have been used to examine tobacco hornworm pupal exuviae labeled either with a combination of [beta-C-13]dopamine and [ring-N-15(2)]histidine or with beta-[3-C-13, N-15]alanine. The spectra are consistent with the incorporation of N-beta-alanyldopamine into insect cuticle by the formation of a variety of covalent bonds. One of these bonds links a histidyl ring nitrogen to a catechol beta-carbon. Other bonds involve the amino group of N-beta-alanyldopamine. These results are interpreted in terms of a general structure for stabilized cuticle that involves cross-linking of proteins to other proteins or chitin through catecholamines.