Effect of calcium ions on the processing of pro-opiomelanocortin by bovine intermediate lobe pro-opiomelanocortin-converting enzyme. |
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Authors: | N P Birch H P Bennett F E Estivariz Y P Loh |
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Institution: | Section of Cellular Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892. |
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Abstract: | The effect of Ca2+ on the extent and pattern of processing of pro-opiomelanocortin and an N-terminal fragment by a purified pituitary secretory vesicle, soluble aspartic endoprotease, was studied. Ca2+ stimulated the first cleavage of pro-opiomelanocortin by pro-opiomelanocortin-converting enzyme to yield 21-23 kDa adrenocorticotropin and beta-lipotropin, but its effect was minimal. The production of adrenocorticotropin from the 21-23 kDa intermediate was stimulated approximately 2.3-fold in the presence of 10 mM Ca2+, and processing of beta-lipotropin to beta-endorphin was stimulated about 1.3-1.4-fold by 5-10 mM Ca2+. The production of gamma-melanotropin-immunoreactive material from bovine N-pro-opiomelanocortin(1-77) was stimulated approximately 1.3-fold at both 100 microM and 1.5-2.0 mM Ca2+. Further characterization of the gamma-melanotropin-immunoreactive material by HPLC demonstrated that the major products were gamma 3-Lys]melanotropin and gamma 3-melanotropin at both Ca2+ concentrations. These results indicate that pro-opiomelanocortin-converting enzyme is stimulated by Ca2+. |
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