The insulin receptor on the human lymphocyte: insulin-induced down-regulation of 126,000 and 90,000 glycosylated subunits.

Cultured human lymphoblastoid B lymphocytes were surface-labelled with iodine125 and solubilized in 1% Triton X-100 in the presence of protease inhibitors. After purification of labelled glycoproteins by elution from immobilized wheat germ lectin with 0.3 mol/l N-acetyl-D-glucosamine, insulin receptors were quantitatively immunoprecipitated using IgG receptor auto-antibodies. The overall recovery of labelled glycoprotein was 0.02-0.04%; analysis by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and autoradiography under reducing conditions revealed two major bands with molecular weights of 126,000 and 90,000, and a minor band of 67,000 daltons. The mobilities of both major receptor subunits were increased after treatment with neuraminidase. When lymphocyte receptor binding was 'down-regulated' before surface labelling, there was a concomitant decrease in the recovery of both the 126,000 and 90,000 subunits. These data indicate that 'down-regulation' of binding probably involves degradation of the receptor molecule.