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Acid extracts of the brain of a urodele amphibian, Ambystoma tigrinum, were screened with radioimmunoassays specific for enkephalin-related products and dynorphin-related products. Following Sephadex G-50 column chromatography a peak of enkephalin-sized immunoreactive material was detected near the total volume of the column. The enkephalin-sized immunoreactivity was further analyzed by reversed phase HPLC. This analysis detected peaks of authentic Met-enkephalin and Leu-enkephalin. However, the molar ratio of Met-enkephalin to Leu-enkephalin in the brain of this amphibian was approximately 80:1. These observations would suggest that the Leu-enkephalin detected in the brain of Ambystoma may be derived from a source other than the Proenkephalin precursor. Neither Met-enkephalin-RGL or Met-enkephalin-RF were detected by radioimmunoassay in brain extracts from this urodele. However, following digestion with trypsin and carboxypeptidase B, a novel peak of C-terminally extended Met-enkephalin was detected. Two peaks of Prodynorphin-related products were also detected following gel filtration chromatography. These immunoreactive forms were detected using antisera specific for alpha-neo-endorphin and dynorphin B(1-13). No immunoreactive forms with antigenic determinants similar to mammalian dynorphin A(1-17) or dynorphin A(1-8) were detected in this species. Reversed phase HPLC analysis indicated that the major form of urodele alpha-neo-endorphin eluted with the same retention time as synthetic mammalian alpha-neo-endorphin. Urodele dynorphin B(1-13)-related immunoreactivity eluted as a single peak, however, this form did not elute with the same retention time as synthetic mammalian dynorphin B(1-13).(ABSTRACT TRUNCATED AT 250 WORDS)

Three distinct opioid precursors have been identified in the central nervous system of mammals: proopiomelanocortin (POMC), proenkephalin, and prodynorphin. These precursors are derived from separate genes, synthesized in distinct neurons, and yield unique sets of opioid end products. This review will discuss the general mechanisms involved in the biosynthesis of neuropeptide precursors and consider the roles of posttranscriptional and posttranslational processing mechanisms in the generation of multiple sets of end products from a single gene. In addition, techniques that can be used for isolating and characterizing neuropeptide genes, mRNAs, and end products will be reviewed. These introductory comments will serve as the framework for a discussion of the phylogeny of the opioid precursors in the major groups of non-mammalian vertebrates.