Plasma membrane receptor for beta-lactoglobulin and retinol-binding protein in murine hybridomas

The aim of the present work was to study the binding of [125I]-BLGA (β-lactoglobulin variant A) to the plasma membrane fraction of hybrid cells. This binding increased as a function of time with on-rate and off-rate constant at 4.47 ± 0.18× 106 M−1 min−1 and 0.17 ± 0.07 min−1, respectively (n = 3). The saturation study showed a single binding site type corresponding to a Kd at 8.26 ± 2.98 nM and 14.02 ± 2.61× 1012 sites per mg of the plasma membrane protein (n = 3). Competitive of binding BLGA was observed with BLGA, complexed with retinol and also with RBP (retinol-binding protein). Gel filtration of [125I]-BLGA incubated with Triton X-100 solubilized membrane showed the formation of a ligand-receptor complex. Cross-linking of the tracer to plasma membrane showed a complex with a Mr at 69 kDa, suggesting a receptor M_r of 51 kDa, as seen by autoradiography of SDS-PAGE.