Measurement of the kinetics of inhibition of activated coagulation factor X in human plasma: The effect of plasma and inhibitor concentration

✍ Scribed by Jolyon Jesty

• Publisher: Elsevier Science
• Year: 1986
• Tongue: English
• Weight: 937 KB
• Volume: 152
• Category: Article
• ISSN: 0003-2697
• DOI: 10.1016/0003-2697(86)90427-6

✦ Synopsis

A method has been developed for detailed kinetic studies of the inhibition of factor X. in human plasma. Radiolabeled enzyme is not required, and the method can be used at initial factor X. levels of 1 nM. The method is discontinuous and based on the removal of samples into an amidolytic assay done in the presence of I% Lubrol-PX detergent. This permits the study of inhibition in mixtures containing phospholipid, platelets, or thromboplastin. The method can be used at inhibition rates in excess of I mitt-', and by suitable analysis can be used to estimate the contribution of inhibition by olz-macroglobulin, which does not itself inhibit amidolytic activity. The method is at present limited to cases where thrombin is not generated in large excess. Factor X, inhibition has been studied in titrated plasma as a function of total plasma concentration, and-by the use of antithrombin-depleted plasma-as a function of the antithrombin concentration of the plasma. In all situations inhibition is characterized by second-order behavior: (i) total inhibition rate is proportional to plasma concentration up to 95%, giving a maximum rate in the absence of calcium of I min-'; " (u) Inhibition in depleted plasma reconstituted with antithrombin shows inhibition rate to remain linearly related to antithrombin concentration; and (iii) the estimated rate due to cuz-macroglobulin is proportional to plasma concentration. It is thus confirmed that, as in pure systems, inhibition of factor X, in whole plasma is linearly related to the concentration of each class of inhibitor. 0 1986 Academic Press, hc.