Identification of transmembrane bridging proteins in the plasma membrane of cultured mouse L cells.

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Abstract
Mouse L-929 cells were grown in suspension culture were 125I-labeled by lactoperoxidase and allowed to ingest latex particles to produce inside-out membrane phagosome preparations. Phagosomes were isolated and the inner membrane surface was labeled with N-(5''-aminopentyl)-5-dimethylamino-1-naphthalenesulfonamide (dansylcadavarine) by a transglutaminase-catalyzed reaction. The phagosome membrane proteins were solubilized and dansylcadavarine-labeled proteins were isolated by anti-dansyl immunoadsorbent affinity chromatography. Dansylcadavarine-labeled proteins were analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and autoradiography for the presence of 125I-labeled material. By this technique, 2 iodinated proteins with MW of .apprx. 50,000 and 80,000 appear to be selectively retained by the anti-dansyl immunoadsorbent, suggesting that these proteins span the plasma membrane.