Affinity labeling of multiplication stimulating activity receptors in membranes from rat and human tissues

Plasma membranes from rat adipocytes and liver and from human placenta have been labeled by covalent cross-linking to membrane-bound 125I-labeled multiplication stimulating activity (125I-MSA) with three different bishydroxysuccinimide esters: disuccinimidyl suberate, disuccinimidyl succinate, and ethyleneglycolyl bis(succinimidyl succinate). Dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiographic analysis of the 125I-MSA-labeled material in the presence of dithiothreitol reveals one single-labeled protein migrating with an apparent Mr = 255,000 regardless of the kind and concentration of cross-linker used. Electrophoresis in the absence of reductant indicates that the affinity-labeled species is not disulfide-linked to any other protein in the native plasma membrane, but contains internal disulfide bonds that compact its structure. The labeling of the Mr = 255,000 species increases with increasing concentrations of 125I-MSA between 0.3 and 3 nM. Labeling is abolished in a competitive manner by nonradioactive MSA but not by similar concentrations of insulin, proinsulin, or epidermal growth factor in all three tissues examined. The unique labeling of this Mr = 225,000 membrane component and its selective inhibition by MSA suggest that this protein is a plasma membrane receptor for MSA.