Effect of NaCl on the association of thrombin with heparin

✍ Scribed by Dr. Genichiro Oshima; Hideki Uchiyama; Kinzo Nagasawa

• Publisher: Wiley (John Wiley & Sons)
• Year: 1986
• Tongue: English
• Weight: 647 KB
• Volume: 25
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360250402

✦ Synopsis

The association of heparin with thrombin was investigated by fluorometric titration. A maximum of 25% of the fluorescence of fluorescein-labeled heparin (FTGheparin) was quenched at thrombin saturation in the absence of NaC1. FTGheparin (H) associated tightly with thrombin (T) and the association constant of the ternary complex, H2T, formed in the absence of NaCl, was calculated to be 1.7 X 108M-l. However, the association was strongly influenced by the NaCl concentration, and the association constant of the equimolar complex, HT, formed in 0.15M NaCl was found to be 1 X 106M-'. The first-order rate constant, k.,,, for inactivation of thrombin by antithrombin 111 (AT 111) and low-affinity heparin (LA-heparin) was comparable with that of highaffinity heparin (HA-heparin) in the absence of NaCI, but decreased with an increase in the concentration of NaCl. The decreased enhancement of the thrombin-AT 111 reaction by LA-heparin at high NaCl concentration appeared to result from a decreased association of thrombin with LA-heparin, thus reducing the formation of the ternary complex, thrombin-LA-heparin-AT 111.