title: Localization of the disulfide bond in human antithrombin III required for heparin-accelerated thrombin inactivation.
abstract: Heparin accelerates the rate of inhibition of thrombin by antithrombin III. Reduction of one of the three antithrombin disulfide bonds with dithiothreitol under mild conditions abolishes this rate-enhancing effect without affecting the rate of reaction in the absence of heparin. Alkylation of mildly reduced antithrombin III with [3H]iodacetic acid followed by digestion with cyanogen bromide yielded two major labeled peptides. The smaller peptide, containing Cys-422, was identified as extending from Gly-414 to the C-terminus, Lys-424. Our data are consistent with the larger labeled peptide being the one extending from Glu-104 to Met-243 and containing Cys-239. Cys-422 has been shown by others to be linked to Cys-239. These data indicate that the sensitive disulfide bond in antithrombin III extends between Cys-239 and Cys-422; the site at which thrombin cleaves the antithrombin III is between these two half-cystines.
mesh_terms: D000990:Antithrombin III / Q000502:physiology*; D001665:Binding Sites; D055598:Chemical Phenomena; D002621:Chemistry; D002851:Chromatography, High Pressure Liquid; D004220:Disulfides / Q000097:blood*; D006493:Heparin / Q000494:pharmacology*; D006801:Humans; D013917:Thrombin / Q000037:antagonists & inhibitors*
chemical_list: D004220:Disulfides; D000990:Antithrombin III; D006493:Heparin; D013917:Thrombin