Delipidation of alpha 1-acid glycoprotein. Propranolol binding to this glycoprotein and its modification by extracted...

Propranolol binding to human alpha 1-acid glycoprotein (AAG) delipidated by two methods is described. Commercial AAG (99% pure) was either precipitated by ethanol-acetone and then washed by ether, or it was precipitated by ethanol. Binding capacity was quantified by the product n x Ka where n denotes the number of binding sites and Ka the association constant (M-1). Propranolol binding to nondelipidated AAG (n x Ka = 0.113 +/- 0.013 microM-1) was clearly increased after precipitation by ethanol-acetone (n x Ka = 0.386 +/- 0.109 microM-1) or precipitation by ethanol (n x Ka = 0.312 +/- 0.096 microM-1). Binding capacity potentiation cannot be due to modification of AAG microheterogeneity forms, as two-dimensional gel electrophoresis pattern of AAG in presence of concanavalin A was not altered after both methods. Recombination of precipitated AAGs with supernatant dry residue resulted in the abrogation of observed potentiation. Moreover, addition of a polar lipid, linoleic acid, (from 30 to 300 microM) strongly inhibited propranolol binding. These results indicated that glycoprotein precipitation by ethanol provided a simple method to further study binding inhibitors associated with isolated AAG.