Figure 2.

 Lack of interaction between Agouti protein and α-MSH assayed by filtration binding. α-MSH (4 nm) was mixed with either 130 nm Agouti protein (○) or 130 nm BSA (▪) in 2 ml of 70% L-15 media, then subjected to 2 hr of filter centrifugation with a 3-kD filter (Centriprep 3, Amicon, Beverly, MA). Serial dilutions of the two filtrates were assayed for pigment dispersion activity, and no differences were apparent between the Agouti protein and the BSA samples. Testing the retentates for pigment dispersion activity (not shown) confirmed that the Agouti protein remained active after the centrifugation.