Proteolytic degradation of neuronal benzodiazepine binding sites

The pathway of breakdown of membrane-bound benzodiazepine binding sites has been examined with proteolytic enzymes. Photoaffinity labeled benzodiazepine receptors were degraded for varying amounts of time and at varying enzyme concentrations. The properties of fractions both remaining in the membrane and released into the supernatant were examined for their apparent molecular weight by SDS gel electrophoresis. Trypsin treatment converted the 46K subunits of the GABA/BDZ complex which bind 3H-flunitrazepam into 40K and 27.5K fragments which remained in the membrane and finally a small fragment which was released into the supernatant. An endogenous trypsin-like activity in the membrane fractions has similar proteolytic effects on the membrane bound receptor.