Analysis of functional agouti protein in the liver of alb-agouti 86 transgenic mice. Functional agouti protein was assayed by its ability to inhibit binding of [125I]-NDP-αMSH to the Mc1r in murine melanoma B16F10 cells. The livers from three alb-agouti 86 mice were excised, pooled, homogenized, and enriched for agouti protein. The livers from three non-transgenic control mice were treated in the same manner (see Methods). The B16F10 cells were incubated for 2 hr at room temperature with 0.1 nM [125I]-NDP-αMSH plus increasing amounts of either partially purified liver homogenate from control mice (control), liver homogenate from alb-agouti 86 mice (alb-agouti 86), or liver homogenate from control mice spiked with recombinant agouti protein (control+agouti). Bound radioactive ligand was measured and plotted (y-axis) against the amount of liver homogenates used in the assay (x-axis).