Biochemical analysis of ligand-induced receptor patching and capping using a novel immunolactoperoxidase iodination technique.

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Abstract
A novel approach for analysis of membrane proteins involved in ligand-induced surface receptor patching and capping was described. The technique was based on the use of immunolactoperoxidase (immuno-LPO) conjugates which catalyze the iodination of those surface proteins with available tyrosine groups located in the immediate vicinity of the patch or cap of a particular antigen. Patching and capping of the H-2 (histocompatibility) antigen on mouse thymocytes was used to illustrate this method. Generally, technique should be applicable to any cell surface proteins which can be induced to form patches or caps by a specific ligand. Cytochemical analysis indicated that the immuno-LPO conjugates induce the same patching and capping of the H-2 antigen as does the unconjugated antibody. Biochemical analysis of 125I-labeled proteins by SDS [sodium dodecyl sulfate] polyacrylamide gel electrophoresis indicated that a large membrane protein (MW of .apprx. 200,000 daltons) is closely associated with H-2 patches and caps. Since other prominent membrane proteins were not labeled by this procedure, selective redistribution of certain surface proteins must occur during H-2 antibody-induced patching and capping.