Processing of enkephalin precursors by chromaffin granule enzymes

Subcellular localization studies indicate that the enzyme activities which cleave enkephalins from larger polypeptides are located in both membranous and soluble components of the chromaffin granules and not in the lysosomes. Cleavage of endogenous precursors produced methionine enkephalin [Met-E], leucine enkephalin [Leu-E], and Met-E-Arg6. Cleavage of synthetic peptide E produced Leu-E, Met-E, and Met-E-Arg6. The pH optimum for enkephalin production is pH 5.7. Dithiothreitol prevents the inhibition of enkephalin conversion produced by p-chloromecurobenzoate. Studies with peptide E indicate that cleavage appears to occur at pairs of basic amino acid residues. The presence of enkephalin producing enzymes with the precursors and the products in the chromaffin granules could be important in the elucidation of the factors that regulate enkephalin biosynthesis.