A highly purified prolactin (PRL) was obtained from pituitary glands of newts, Cynops pyrrhogaster, by extraction of acetone-dried powder with acid acetone and high-performance liquid chromatography (HPLC) on Mono-Q (anion exchange), Superose-12 (gel filtration), and TSK-gel ODS-120T (reverse-phase) columns with a yield of 4.5 mg per 325 mg of protein starting material. Purification was monitored by SDS-polyacrylamide gel electrophoresis (PAGE) and Western blotting analysis employing antiserum against bullfrog PRL. Newt PRL thus obtained has a molecular weight of 23,000 as determined by SDS-PAGE. The isoelectric point is 4.7 as determined by isoelectric focusing. The amino acid composition closely resembles that of anuran PRLs. This hormone was as potent as bovine PRL in stimulating collagen synthesis in the bullfrog tadpole tail fin. Antiserum against newt PRL was produced by immunizing a rabbit. Histological studies on newt adeno-hypophyses revealed that the cells that immunologically reacted with the antiserum against newt PRL correspond to the ones positively stained with the antiserum against bullfrog PRL.
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