One of two subunits of masking protein in latent TGF‐β is a part of pro‐TGF‐β

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Abstract
A high molecular mass latent form of transforming growth factor type‐β (TGF‐β) was purified to homogeneity from rat platelets by a seven‐step procedure involving group‐specific affinity chromatographies on Red‐Toyopearl and zinc chelating‐Sepharose. The purified latent TGF‐β was a complex of TGF‐β (25 kDA) and the binding protein previously named masking protein (∼400 kDA) [(1986) Biochem. Biophys. Res. Commun. 141, 176–184]. Analysis of the peptide structure by gel electrophoresis showed that the masking protein consisted of two subunits of 39 kDA and 105–120 kDA linked by disulfide bonds. N‐terminal amino‐acid sequencing of the 39 kDA subunit indicated that this subunit was identical to the N‐terminal part of the TGF‐β precursor.