%0 Journal Article
%T The Modification of Xa-ATIII-Heparin Dynamics by Protamine Sulfate
%A Martin H. Coggin
%A Arthur S. Brecher
%J ISRN Cell Biology
%D 2012
%R 10.5402/2012/632867
%X Heparin promotes the formation of 1ˇă FXa¦Á-ATIII and FXa¦Â-ATIII complexes from the free enzymes and antithrombin III. It further stimulates the transformations of the 1ˇă complexes into the corresponding 3ˇă complexes. Additionally, it stimulates the degradation of the 1ˇă FXa¦Á-ATIII and FXa¦Â-ATIII complexes into free FXa¦Á, FXa¦Â and ATIIIM. Protamine sulfate (PS) stimulates the transformation of FXa¦Á into FXa¦Â and hence to FXa¦Ă. It also stimulates the transformation of the 1ˇă-, 2ˇă-, and 3ˇă- FX¦Á-ATIII complexes into their corresponding ¦Â-complexes. It further promotes the degradation of the 1ˇă FXa¦Á- and FXa¦Â-ATIII complexes into their corresponding 3ˇă- FXa¦Á- and FXa¦Â-ATIII complexes, with the concommittant release of FXa¦Ă. The addition of PS to FXa/ATIII/H mixtures results in a reduction in free FXa, ATIII, and 1ˇă Xa-ATIII complex formation, together with the concommittant increase in 3ˇă-FXa- ATIII complex formation and release of FXa¦Ă. The likeliest explanation of these results resides in the removal of the effective free heparin as a consequence of the generation of a stable heparin/PS salt upon the addition of the PS to the FXa/ATIII/H mixtures, thereby effectively lowering clotting times. 1. Introduction Factor X is located at the juncture of the intrinsic and extrinsic coagulation cascade pathways. Factor X has two active forms (FXa¦Á and FXa¦Â) that differ in molecular weight by about 4000 daltons. Factor Xa¦Â can be degradatively inactivated (autolyzed) to form FXa¦Ă upon cleavage at the ¨CNH2 terminal of the active site [1¨C3]. The serpin antithrombin III (ATIII) is the primary naturally occurring inhibitor of Factor Xa. Factor Xa and antithrombin III form a 1Łż:Łż1 molar complex via covalent bonding [3¨C5]. Upon hydrolysis of this bond, a modified form of ATIII is produced (ATIIIM). ATIIIM runs at a slightly higher apparent molecular weight than native ATIII in SDS-PAGE [3, 5, 6]. The polysulfonated glycosaminoglycan heparin (H) is administered clinically as an anticoagulant. H acts to catalyze interactions of ATIII with factors Xa and IIa, among other coagulation factors. Heparin fractions have varying affinity for ATIII, with the smallest fraction of high affinity being the pentasaccharide. Administration of H increases the FXa-ATIII complex formation by at least an order of magnitude [7] or several hundredfold when also in the presence of physiological levels of Ca2+[8¨C10]. Further, ATIIIM increases 20¨C30% in the presence of FXa and high-affinity heparin [6, 11]. Positively charged protamine sulfate (PS) has long been used clinically to neutralize heparin
%U http://www.hindawi.com/journals/isrn.cell.biology/2012/632867/