Differential mechanisms for the N-acetylation of alpha-melanocyte-stimulating hormone and beta-endorphin in the intermediate pituitary of the frog, Xenopus laevis.
Immunohistochemical analysis of the pituitary of Xenopus laevis revealed the colocalization of alpha-melanocyte-stimulating-hormone (MSH)-related immunoreactivity and N-acetyl-beta-endorphin-related immunoreactivity in the cells of the intermediate pituitary. In order to determine whether the immunoreactive N-acetylated beta-endorphin is released in parallel with the immunoreactive alpha-MSH, intermediate pituitaries were incubated in L-15 medium for 24 h. The medium and an acid extract of the intermediate pituitaries from each incubation were separately fractioned by a combination of gel filtration chromatography, reverse-phase high-performance liquid chromatography, and cation exchange chromatography. In the intermediate pituitary extract, the major form of alpha-MSH had chromatographic properties which corresponded to nonacetylated alpha-MSH (ACTH)(1-13)amide; whereas the major form of beta-endorphin had an apparent molecular weight of 1.2 kDa and was N-acetylated. The 1.2-kDa form of beta-endorphin and ACTH(1-13)amide were present in equimolar amounts. Analysis of the medium indicated that both end products were released in parallel. However, as reported in the literature, there was a significant increase in the N-acetylation of ACTH(1-13)amide during secretion. There was no further processing of beta-endorphin during secretion. Collectively, these observations indicate that in the intermediate pituitary of X. laevis there are separate mechanisms for the N-acetylation of alpha-MSH and beta-endorphin.
Dores
R M
RM
Department of Biological Sciences, University of Denver, Colo.
Steveson
T C
TC
Lopez
K
K
D000107:Acetylation; D000818:Animals; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D005260:Female; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D008297:Male; D010446:Peptide Fragments / Q000378:metabolism; D010902:Pituitary Gland / Q000378:metabolism*; D011333:Pro-Opiomelanocortin / Q000378:metabolism; D011863:Radioimmunoassay; D014982:Xenopus laevis; D000521:alpha-MSH / Q000031:analogs & derivatives / Q000378:metabolism*; D001615:beta-Endorphin / Q000378:metabolism*
D010446:Peptide Fragments; D000521:alpha-MSH; D001615:beta-Endorphin; D011333:Pro-Opiomelanocortin