SERINE DECOMPOSITION IN SOLID-STATE CATALYTIC ISOTOPE EXCHANGE OF A PEPTIDE

In connection with work related to cAMP-dependent protein kinase, a tritiated substrate, Arg-Arg-Ala-Ser-Val-Ala, was prepared from the corresponding unlabeled peptide by solid-state catalytic isotope exchange. Varying amounts of side products with chromatographic properties very similar to those of the substrate were observed. Careful chromatographic comparison with a complete set of diastereomers eliminated racemization as the reason for this heterogeneity. Instead, the serine residue was identified as the major source of by-products, presumably due to primary elimination of water followed by saturation of the dehydroalanine residue, transforming it into a racemic alanine, thus giving rise to Arg-Arg-Ala-(d, l-Ala)-Val-Ala. © 1992.