Purification of a mammary-derived growth inhibitor (MDGI) related polypeptide expressed during pregnancy

The present study was undertaken to screen immunochemically for MDGI-related proteins in the mammary gland. A new form, MDGI 2, not present in lactation could be detected in the bovine gland during pregnancy. It was further distinguished from MDGI by its lower molecular weight, its association with a complex binding to WGA, and by lacking immunoreactivity to an anti-MDGI antibody directed against the C-terminus of MDGI. MDGI 2 was purified by chromatography over DEAE-Sepharose, Bio-Gel P-30 in 1% acetic acid, Sephacryl S-200 in 6 M urea and Mono Q. Final purification included HPLC on TSK G-3000 SW and electroelution from SDS-gels. Cell-free translation of poly (A+)mRNA from glands of pregnant animal yielded one form identical with MDGI. We assume that posttranslational processing of MDGI is involved in its activities.