Dermorphin, a heptapeptide with very potent opiate‐like activity, has been isolated from methanol extracts of the skin of the South American frog Phyllomedusa sauvagei. The amino acid sequence of the peptide is: H‐Tyr‐D‐Ala‐Phe‐Gly‐Tyr‐Pro‐Ser‐NH2. Dermorphin presents striking differences from the known enkephalins; it offers a surprising example of a peptide from Vertebrata containing a D‐amino acid residue in its sequence.
The proton NMR characterization of bombesin has been carried out at 500 MHz in DMSO-d, using twodimensional homo-and 'H-'V hetero-correlated techniques. All resonances in the NMR spectra have been assigned and several coupling constants have been measured. The backbone JaCH+,,, coupling constants have constant values that vary between 7.8 and 8.2 Hz and indicate an unfolded structure in DMSO-4. Discrepancies with data recently obtained at 300 MHz [(1987[( ) Eur. J. B&hem. 168, 193-1991
The reaction between the cyclic dianhydride of diethylenetriaminepentaacetic acid (DTPA), a bifunctional reagent, and proteins under various conditions was studied using porcine insulin as a model protein. The reaction was compared with that between citraconic anhydride, a monofunctional reagent, and insulin. Products were characterized chromatographically and electrophoretically before and after deesterification by hydroxylamine. A DTPA-conjugated product was further characterized by proteolytic fragmentation. The reaction with citraconic anhydride yielded the expected number of products exclusively acylated on amino groups. In contrast, the reaction with the cyclic dianhydride of DTPA under all conditions examined yielded a much higher number of products than expected. Among the products formed were O-acylated ones and products of intermolecular cross-linking. It is concluded that the use of the cyclic dianhydride of DTPA does not allow the reliable preparation of proteins or other macromolecules conjugated with a high number of DTPA molecules in which each molecule of DTPA is linked to one amino group of the macromolecule through a single amide bond.
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