Characterization of the molecular forms of proenkephalin in bovine adrenal medulla and rat adrenal, brain, and spinal cord with a site-directed antiserum

An antiserum was generated against a synthetic peptide corresponding to amino acids 95-117 of bovine proenkephalin, and a sensitive radioimmunoassay was developed. Comparison of the reactivities of the synthetic peptide, its specific cleavage products, and other synthetic peptides showed that the important immunological determinant was contained within residues 101-109 of bovine proenkephalin (-Gly-Gly-Glu-Val-Leu-Gly-Lys-Arg-Tyr-). Radioimmunoassay of fractions after gel filtration of bovine adrenal medullary chromaffin granule lysate showed three pools of immunoreactivity: pool 1 (Mr 20,000-30,000), pool 2 (Mr 10,000-20,000), and pool 3 (Mr approximately 5,000). Further characterization by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by immunoblotting showed that the antiserum recognized 27-, 20.5-, 16.5-, and 5.6-kilodalton enkephalin-containing proteins. The radioimmunoassay was also used to detect proenkephalin-like material in extracts of rat adrenal and regions of rat brain and spinal cord following gel filtration. Immunoreactivity from the rat adrenal chromatographed predominantly as high molecular weight material (Mr 31,500-43,500), whereas material in regions of rat brain showed a broader molecular weight distribution (Mr 4,000-43,500). This indicated differences in the processing of proenkephalin between rat adrenal and brain tissue. Differences were also seen in the molecular weight profile of immunoreactivity in different brain regions, most noticeable in the case of striatum and hypothalamus, suggesting regional differences in processing. Based on quantitation of higher molecular weight immunoreactive proenkephalin-like material and free Met-enkephalin immunoreactivity in different brain regions, it was apparent that extensive processing of proenkephalin occurs in brain. We concluded that antisera against proenkephalin-(95-117) recognize a wide range of intermediates in the processing of proenkephalin in both bovine adrenal medulla and rat adrenal, brain, and spinal cord, making it a useful tool for further studies concerned with the expression and post-translational processing of proenkephalin.