Figure 3.

Comparison of the profiles of neonatal rat serum proteins that were immunoprecipitated and immunoblotted with a polyclonal anti-M6P/IGF-II receptor antibody and an anti-peptide antibody against the cytoplasmic domain (provided by R. G. MacDonald; ref. 23). (A) Immunoprecipitation. Two equivalent aliquots of neonatal rat serum proteins were precipitated with either antibody as described in Methods. The anti-receptor antibody precipitated both a 300- and a 260-kDa protein (lane 1), whereas the anti-peptide antibody precipitated the 300-kDa protein only (lane 2). (B) Western immunoblotting. Aliquots of neonatal rat serum were electrophoresed under nonreducing condition (lanes 1 and 2, both are the same blot) or after reduction with 5% 2-mercaptoethonal (lane 3). Electrophoresed proteins were transferred to nitrocellulose and probed with the anti-receptor antibody (lane 1) or the anti-peptide antibody (lanes 2 and 3). A 300-kDa protein, which did not change with disulfide bond reduction, was recognized by both antibodies, whereas a 220-kDa protein (under nonreducing condition) was recognized by the anti-receptor antibody only.