Synthesis and use of peptide substrates for the isolation and characterization of proenkephalin processing enzymes

Classical methods of peptide synthesis in solution were used for the preparation of the two tetrapeptides alanyl-lysyl-arginyl-tyrosine and acetyl-alanyl-lysyl-arginyl-tyrosine-(N-methylamide). The two compounds were able to be recognized as substrates by proenkephalin processing enzymes and were used for the development of a quantitative assay for these enzymes. The first substrate proved to be convenient, although it was also partially degraded by amino- and carboxypeptidases under the conditions of the assay. The second was found to be hydrolyzed by the endopeptidases at too slow a rate to allow its routine use in the assay.