Characterization of binding of transforming growth factor-beta 1 to bovine mammary membranes

This study developed a procedure to measure binding of transforming growth factor-beta 1 to bovine mammary membranes. Mammary membranes were incubated with 3 M MgCl2 to remove endogenously bound transforming growth factor-beta 1. Binding was optimized by incubation of 200 micrograms of membrane protein with 125I-labeled transforming growth factor-beta 1 in 25 mM Tris, 10 mM CaCl2, and 1.0% BSA in a total volume of .5 ml in the presence or absence of unlabeled transforming growth factor-beta 1. The reaction equilibrated in 2 h at 4 degrees C. Specific binding was linear from 142 to 1140 micrograms of membrane protein. The reaction was specific for the beta transforming growth factors; transforming growth factor-beta 1, transforming growth factor-beta 2, and transforming growth factor-beta 3 could complete effectively with 125I-labeled transforming growth factor-beta 1 for the receptor. The growth factors, epidermal growth factor, IGF-I, or transforming growth factor-alpha did not compete effectively with 125I-labeled transforming growth factor-beta 1 for binding to bovine mammary membranes. Scatchard analysis showed that the number of receptors averaged 251 pmol/mg of membrane protein and the affinity was 8.7 x 10(-11) M. Binding to mammary membranes was higher during the prepubertal and pubertal periods than during lactation. Binding to mammary membranes during early lactation averaged 24% of the binding observed during other physiological states.(ABSTRACT TRUNCATED AT 250 WORDS)