The M r 80,000 common forms of neurophysin and vasopressin from bovine neurohypophysis have corticotropin- and β-endorphin-like sequences and liberate by proteolysis biologically active corticotropin

Abstract

We have tested the hypothesis that the high M_r forms common to both neurophysin and vasopressin detected in bovine neurohypophysis extracts (Nicolas, P., Camier, M., Lauber, M., Masse, M.-J. O., Möhring, J. & Cohen, P. (1980) Proc. Natl. Acad. Sci. USA 77, 2587-2591) might also contain the sequences of other known neuropeptides. The following evidence indicates that corticotropin- and β-endorphin-like sequences are associated with similar high M_r forms and are included in these M_r 80,000 molecules. During the fractionation steps of high M_r material, both corticotropin and β-endorphin immunoreactive species were found to coelute with the neurophysin and vasopressin ones, either under M_r 140,000 (in 0.1 M formic acid) or M_r 70,000-80,000 (in 6 M guanidine) elution volumes. Corticotropin immunoreactivity was found to cofocus at pIs 6.05 and 5.8 with the M_r 80,000 neurophysin-containing species. This material was submitted to affinity chromatography on purified anti-neurophysin antibodies covalently attached to Sepharose 4B. Both the corticotropin and β-endorphin immunoreactivities, together with the neurophysin and vasopressin immunoreactivities, were retained on the immunoadsorbent and codesorbed by either a drastic pH change or by selective displacement with an excess of neurophysin. Comparison of the tryptic-digest maps of either the M_r 68,000 fragment immunoprecipitated by anti-corticotropin antibodies or the M_r 68,000 fragment released after precipitation of the M_r 80,000 species by anti-neurophysin antibodies indicated large sequence homologies. Exposure of either the M_r 80,000 or 68,000 components to mild proteolytic activities resulted in the formation of lower-size fragments. The resulting corticotropin-like immunoreactive material, recovered under the elution volume of standard ¹²⁵I-labeled corticotropin-(1-24), was tested for its ability to activate glucocorticoid biogenesis by the amphibian interrenal tissue (adrenal) in perifusion. It was found to exhibit a noticeable activity qualitatively undistinguishable from the one of the reference human corticotropin-(1-39). The name neurohypophyseal “coenophorin” (from the Greek word for common) is proposed for this class of M_r 80,000 polypeptides that might represent the common precursor store-house for a set of neuropeptides produced in the hypothalamo-neurohypophyseal tract.