Patent ID: 7202043

Claim:
A method for determining endocytic changes of a cell membrane receptor in cells as a result of a change of environment of said cells, where said cells have a labeled cell membrane receptor, said label being (1) bound to said cell membrane receptor, (2) a first member of a specific binding pair and (3) external to said cell membrane, and said method including as a reagent a complementary member of said specific binding pair joined to a member of an enzyme fragment complementation pair, which when complexed to a complementary enzyme fragment forms an active enzyme, said method comprising: adding said reagent to said cells, wherein said reagent becomes bound to said labeled cell membrane receptor; producing an environment to be tested for its effect on endocytosis for said cells to which said reagent is bound; inactivating any of said member of said enzyme fragment complementation pair with an inactivating agent that does not adversely affect the activity of any member of said enzyme fragment complementation pair that has undergone endocytosis; deactivating said inactivating agent; lysing said cells; adding said complementary enzyme fragment and a substrate; and determining the amount of product produced from said substrate; wherein the amount of product is related to the amount of endocytosis of said cell membrane receptor.