Fig. 2. Synapsin I from NRK cells and rat brain show similar phosphopeptide patterns. (A) Synapsin I immunoprecipitated from NRK cells was phosphorylated in vitro by PKA. By autoradiography, a phosphorylated species was detected that co-migrated with rat brain synapsin I and was labeled by SNT1 in immunoblot (*, lanes 1,4). The signal was absent if the anti-synapsin I antibody or the NRK extract were absent during the immunoprecipitation (lanes 2,3). (B) The PKA-phosphorylated proteins were digested with V8 endoprotease or chymotrypsin, the fragments were resolved on a 15% gel, transferred to nitrocellulose and exposed to autoradiographic film. The phosphopeptide maps for both synapsin I purified from rat brain and synapsin I immunoprecipitated from NRK cells are identical. Position of molecular mass standards (in kDa) is indicated.