L to D amino acid isomerization in a peptide hormone is a late post-translational event occurring in specialized neurosecretory cells

Modification of the chirality of a single amino acid residue within a pepti de chain appears to be novel additional mechanism leading to structural and functional diversification of eukaryotic bioactive peptides. This phenomen on has been studied at the cellular level in a neuroendocrine organ which e laborates a mixture of diastereoisomers of a 72-residue neuropeptide, crust acean hyperglycemic hormone. For the first time, amino acid isomerization h as been shown to occur in the perikarya of fully specialized neurosecretory cells, as a late step of the maturation of the hyperglycemic hormone precu rsor and after propeptide cleavage. The specificity and efficiency of this phenomenon indicates the existence of a new enzyme family involved in the b iogenesis of peptide hormones.