Studies of separation and characterization of acetylcholine receptor labeled with tritiated dibenamine

Purification of histamine receptor (VI). An improved double labeling method with "double protection"

Studies were done on the specific labeling of the histaminergic H1-receptor of the longitudinal smooth muscle of cat small intestine. A procedure involving 'double protection' combined with the double labeling technique was developed. The first protection was the usual with a protective antihistamine, promethazine, and the second was cross protection of non-specific sites with non-hitaminergic drugs, thioriazine and atropine. Muscle tissue protected with promethazine against non-radioactive dibenamine was treated with 3H-dibenamine in the presence of these second protectors. The second protectors covered non-receptor sites which had been protected from non-radioactive dibenamine with promethazine. The dose-response curves were carefully checked in each experiment to confirm that the second protectors did not interfere with the specific coverage provided by the first protector. Finally 14C-dibenamine was applied to measure non-specific binding after which the labeled muscles were fractionated and the radioactivity was counted. The specificity of labeling achieved in the receptor-rich fraction by this method is discussed.

Inhibition of alpha-chymotrypsin by dibenamine

α-Chymotrypsin is rapidly inhibited by an acid solution of dibenamine in an irreversible manner when the reactants are mixed in a buffer at near neutral pH. The degree of inhibition depends on the molar ratio of the reactants. The alkylating species is probably the ethyl-eniminium ion from dibenamine, this ion being present at a higher level in the acid media than in the near neutral media used here.

Binding of N-(2-bromo ethyl)-N-ethyl-N 1 -naphthylmethylamine HBr (SY28) to the proteins of guinea-pig vas deferens

1. Vasa deferentia from guinea-pigs were exposed to (14)C-SY28 HBr (5.32 x 10(-6)M) washed, lipid extracted, and broken up.2. The tissue was digested with papain, hydrolyzed with 6 N HCl, and gel filtration performed.3. Aliquots at each stage were used for paper chromatography and autoradiography.4. Three labelled spots (in addition to unbound 2-halogenoalkylamine) were located from acid hydrolysate and a fourth from gel filtrate.5. Selected amino-acids were complexed with (14)C-SY28 and the procedure repeated. The R(F) values were compared with those of the same amino-acids with and without 6 N HCl.6. Histidine, aspartic acid, arginine and serine gave a significant degree of binding of (14)C-SY28.7. The theoretical implications are discussed.