Purification and properties of a human plasma endogenous modulator for the platelet tricyclic binding/serotonin transport complex.
An endogenous modulator for the site labeled by [3H]imipramine which is putatively coupled to the serotonin transporter in human platelets was isolated and purified from plasma. Procedures included sequential chromatography on Cibacron blue-Sepharose 4B, concanavalin A-Sepharose 4B, Mono Q HR 10/10 anion exchange, DuPont GF-250 gel permeation and Mono S HR 5/5 cation exchange columns. The purified modulator is a protein of Mr 45,000 with a very acidic pK (less than 3) and sensitive to various proteinases but heat- and acid-stable. This protein inhibited [3H]imipramine binding to platelet membranes competitively (IC50 approximately 6 microM) and enhanced serotonin uptake in fresh human platelets (EC50 approximately 7 microM). Various physicochemical properties, including chromatographic, electrophoretic and immunological as well as amino acid composition analysis revealed that the isolated protein is most probably the human alpha 1-acid glycoprotein.
D000596:Amino Acids / Q000032:analysis; D001667:Binding, Competitive; D001692:Biological Transport; D001792:Blood Platelets / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002845:Chromatography; D006801:Humans; D007099:Imipramine / Q000097:blood*; D008970:Molecular Weight; D009961:Orosomucoid / Q000302:isolation & purification / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism; D012701:Serotonin / Q000097:blood*
D000596:Amino Acids; D009961:Orosomucoid; D012701:Serotonin; D010447:Peptide Hydrolases; D007099:Imipramine