Growth stimulating activity in bovine pituitary extract specific for a rat mammary carcinoma cell line

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Abstract
We report the isolation of a bovine pituitary growth factor (MGF) for a rat mammary carcinoma cell line, 64‐24, which was isolated from a highly hormone‐dependent mammary tumor. The MGF has been partially purified by a series of Diaflo ultrafiltration membrane sievings, isoelectric focusing and Sephadex columns. The MGF has a molecular weight of ∼︁ 1,000 to 2,000 daltons and has a U.V. absorption spectrum typical for a polypeptide. Its isoelectric point is ∼︁ pH 3.8–4.0. The factor is heat stable. The growth stimulating activity of the MGF does not stimulate other rat cell lines (22‐1, RMG or HTC lines) but is specific for the 64‐24 mammary tumor cell line. The MGF is not among previously reported pituitary hormones or growth factors.