Transforming growth factor beta in bovine milk: concentration, stability and molecular mass forms.
Transforming growth factor beta (TGF-beta) is one of the predominant growth factors present in milk. The concentration, molecular mass forms and stability of TGF-beta in bovine milk were investigated using a standard bioassay measuring the growth inhibition of a milk lung epithelial cell line. Most of the TGF-beta bioactivity in milk was found to be in a latent form, which was also retained in the whey fraction. After acid activation, the total TGF-beta concentration was 4.3 +/- 0.8 ng and 3.7 +/- 0.7 ng TGF-beta per ml of milk and cheese whey respectively. Cation-exchange chromatography at pH 6.5 was used to concentrate latent whey-derived TGF-beta, which could be activated by transient exposure to extremes of pH, urea or heat. Heparin did not significantly activate milk-derived TGF-beta. Neutral gel filtration of the cationic whey fraction revealed a major peak of latent TGF-beta with a molecular mass of 80 kDa and a smaller peak at 600 kDa. Transient acidification of the cationic whey fraction prior to neutral gel filtration, or gel filtration under acidic conditions, released low molecular mass TGF-beta from both high molecular mass peaks. Whey-derived TGF-beta was purified using a five-step chromatographic procedure. An N-terminal sequence was obtained for TGF-beta 2, which accounted for over 85% of the TGF-beta bioactivity in whey. All TGF-beta activity in whey could be neutralised by a monoclonal antibody directed against TGF-beta 1, -beta 2 and -beta 3. The results suggest that the majority of TGF-beta in bovine milk is present in a small latent complex.
Rogers
M L
ML
Cooperative Research Centre for Tissue Growth and Repair, Adelaide, Australia.
Goddard
C
C
Regester
G O
GO
Ballard
F J
FJ
Belford
D A
DA
D000818:Animals; D001681:Biological Assay; D002417:Cattle / Q000378:metabolism*; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D005260:Female; D007536:Isomerism; D008892:Milk / Q000737:chemistry / Q000378:metabolism*; D008970:Molecular Weight; D016212:Transforming Growth Factor beta / Q000032:analysis* / Q000737:chemistry
D016212:Transforming Growth Factor beta