A cell line that differentiates into pigment cells when treated with the growth factor called "steel factor." You suspect that steel factor regulates melanogenesis through a receptor tyrosine kinase. Although the receptor is not yet identified, you do by chance happen to have an antibody that when applied to the cells interferes with steel factor-induced melanogenesis. This antibody does not recognize steel factor. Also you have a large supply of purified steel factor that is GST-tagged. How might you purify the receptor and determine if it is a receptor tyrosine kinase?