A new immunological approach to the detection and the quantitation of the Met5-enkephalin precursors in rat brain.

We describe a new approach to the detection and quantitation of the enkephalin precursor. The approach is based on the production of antibody against a sequential determinant which is obtained specifically and quantitatively from the enkephalin precursor by tryptic hydrolysis. We chose the hexapeptide Tyr-Gly-Gly-Phe-Met-Arg and developed antibody against the C-terminus of this peptide. The hexapeptide is released from the precursor by mere tryptic cleavage. The antibody permits us to detect the Met-enkephalin precursor at the picomole level. Using this approach, we have quantitated the precursor forms in rat striatum and hypothalamus. The precursor/Met-enkephalin ratio was close to 3/4. This result was in very good agreement with the ratio determined previously in the bovine adrenal medulla.