STUDIES ON THE PITUITARY MELANOPHORE-EXPANDING HORMONE WITH REFERENCE TO ITS IDENTITY WITH ACTH

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Abstract
SUMMARY: 1. A number of melanophore-expanding (B) extracts of the pituitary have been subjected to electrophoresis on filter-paper, and the resulting pattern of activity assayed, using Xenopus. At pH 7·2, in phosphate buffer, a simple extract of ox posterior lobe powder (OxPLP) shows the greatest range of mobilities. The faster moving components are absent from an acetone precipitated powder (APP), and also from OxPLP after treatment by heating in alkali. An ACTH preparation (Acton) had relatively more faster moving components with B activity than APP or alkali and heat-treated OxPLP. 2. There was no difference in the electrophoretic pattern of APP and alkali and heat-treated APP when examined in barbiturate buffer at pH 8·5. Under these conditions Acton showed a fast moving major peak of activity coincident with the ovalbumin spot. Acton also gave a faster moving component when run at pH 8·8 in barbiturate buffer than an alkali and heattreated OxPLP extract purified by adsorption to and elution from activated charcoal. 3. In acetate buffer all the extracts examined had an isoelectric point close to pH 4·8. 4. It is suggested that the melanophore-expanding activity of single acetic acid extracts of OxPLP is complex. Heating at a high pH for a few min destroys the components in this complex which show highest mobility at a slightly alkaline pH. The melanophore-expanding activity in Acton is probably largely identical with these heat unstable components.

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