Proteolytic degradation routes for turkey β₁-adrenoceptor probed with antipeptide antibodies against the N-terminal sequence of the receptor

Anti-peptide antibodies, raised against the N-terminal sequence (amino acids 2-10) of the turkey β₁-adrenoceptor [Yarden et al., Proc. Natl. Acad. Sci. USA (1986) 83, 6795-6799] recognized the 50 kDa- but not the 40 kDa-form of the receptor, thus confirming the previous assumption that the N-terminus of the 50 kDa form is lost during its conversion to the 40 kDa-form [Jürß, R., Hekman,M. & Helmreich, E.J.M. (1985) Biochemistry 24, 3349-3354]. By in situ proteolysis small amounts of receptor fragments were formed, which could be recognized by the N-terminus specific antibody. Therefore, although the production of the stable 40 kDa receptor species by proteolytic removal of a portion of the N-terminal appears to be the predominant route, there exists an additional pathway of degradation which must involve the initial cleavage of the carboxyl terminal.