Studies on the Rat Hepatic Glucagon Receptor

Treatment of liver plasma membranes with CHAPS was shown to yield glucagon receptor in a soluble, active form. Characterisation of the CHAPS- solubilised receptor using sucrose density gradient centrifugation and gel filtration on Sepharose CL-6B showed that it exists predominantly in a highly aggregated form, and that this aggregation is specific and unchanged by alterations to the detergent concentration or ionic strength. The smallest molecular weight species for the receptor in CHAPS was determined to be ~190 kDa and this is proposed to be a trimer of the hormone binding subunit. Isolation of the active, CHAPS-solubilised receptor was attempted using affinity chromatography with immobilised glucagon, prepared by coupling bromoacetylated BioGel P-150 to the met-25 residue of glucagon. Specific binding of the receptor to the affinity gel was demonstrated. However, various elution methods (with glucagon, urea or low pH buffers) did not yield active receptor. Attempts to elute the receptor with SDS followed by characterisation on SDS- PAGE were unsuccessful due to background non-specific binding to the affinity matrix of the majority of proteins present in the CHAPS extract. Thermostability studies on the CHAPS-solubilised receptor, showing biphasic decay at 3