Distribution and characterization of synenkephalin immunoreactivity in the bovine brain and pituitary

The distribution of synenkephalin, the N-terminal fragment of proenkephalin, was studied in various parts of the bovine brain (globus pallidus, caudate nucleus, hypothalamus) and in the posterior pituitary by the use of a radioimmunoassay. The distribution of synenkephalin-immunoreactivity (IR) was compared to the distribution of Met-enkephalin-IR. Gel exclusion chromatography was used to examine the molecular forms of the immunoreactivities present in the tissues. The distribution of synenkephalin-IR was similar to the distribution of Met-enkephalin-IR, with a molar ratio of Met-enkephalin/synenkephalin ranging between 2.7 and 5.9. In all regions tested except the hypothalamus the synenkephalin-IR was present as a single species. However, in the hypothalamus a small amount of IR material (3% of the total synenkephalin-IR) was detected in fractions where larger Met-enkephalin-containing peptides eluted. Based on the concordance between the molar ratio of Met-enkephalin to synenkephalin found in the tissues and the molar ratio present in the sequence of adrenal proenkephalin, it is concluded that the brain and adrenal glands utilize a similar precursor for enkephalin biosynthesis.