Kinetics of reaction between human activated complement c 1 esterase inhibitor and activated complement c 1r or activated complement c 1s
Nilsson, T.; Wiman, B.
European Journal of Biochemistry 129(3): 663-668
1983
ISSN/ISBN: 0014-2956 Accession: 005784332
The kinetics of the reactions of [human] C.hivin.1[activated complement component 1]-esterase inhibitor with C.hivin.1s or C.hivin.1r were studied in purified sytems. Both reactions proceed in 2 steps: a fast reversible 2nd-order reaction followed by a slower irreversible 1st-order transition according to the following scheme: .**GRAPHIC**. The rate constant k1 for the reaction between C.hivin.1s and C.hivin.1-esterase inhibitor was 1.4 .times. 105 M-1 s-1 at 25.degree. C and 4.7 .times. 105 M-1 s-1 at 37.degree. C, while the corresponding values for the reaction between C.hivin.1r and C.hivin.1-esterase inhibitor were 2.5 .times. 103 M-1 s-1 and 4.4 .times. 104 M-1 s-1, respectively. The dissociation constant K of the initial complex was estimated as 1-2 nM for the complex with C.hivin.1s and 20-50 nM for the complex with C.hivin.1r. Heparin accelerated the rate of the C.hivin.1s/C.hivin.1-esterase inhibitor reaction by a 16-fold increase in k1 at heparin concentrations above 100 mg/l, whereas no effect was obtained on the thermodynamic equilibrium. The inhibition of purified C.hivin.1s added to dilutions of plasma or serum proceeded as expected from their known concentrations of C.hivin.1-esterase inhibitor and the rate constants determined in the purified system. The half-life of C.hivin.1s in plasma under pseudo 1st-order kinetics would be about 1 s.