Unique reactive site domains of neuroendocrine isoforms of alpha1‐antichymotrypsin from bovine adrenal medulla and pituitary revealed by molecular cloning

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Abstract
Molecular cloning of bovine adrenal medulla (AM) and pituitary (Pit)α1‐antichymotrypsin cDNAs indicated novel isoforms of ACT. The deduced primary sequences indicated that the AM ACT and Pit ACT possess COOH‐terminal reactive‐site domains that are characteristic of serpins (serineproteaseinhibitors). Of high interest was the finding of unique reactive sites within AM ACT and Pit ACT which are predicted to possess Arg as P1 residue. Arginine as P1 residue parallels the cleavage specificity of neuroendocrine prohormone processing enzymes cleaving at basic residues. Furthermore, RT‐PCR indicated tissue‐specific expression of AM and Pit ACT mRNAs. The AM and Pit isoforms of ACT may regulate novel target proteases involved in neuroendocrine function.