A Sensitive, Colorimetric Method for the Measurement of Serum C1̄ Inactivator Using the Substrate N-α-Acetyl-L-Lysine Methyl Ester
Open Access
- 1 April 1970
- journal article
- Published by Oxford University Press (OUP) in The Journal of Immunology
- Vol. 104 (4) , 1024-1030
- https://doi.org/10.4049/jimmunol.104.4.1024
Abstract
A sensitive, colorimetric procedure for measuring the serum inhibitor of the first component of complement, C1̄ inactivator, has been developed. The assay, which is suitable for multiple determinations, is based on the inhibition by C1̄ inactivator of C1s̄-catalyzed hydrolysis of the synthetic ester substrate N-α-acetyl-L-lysine methyl ester. Whole serum or purified inhibitor stoichiometrically blocked the esterolytic activity of C1̄ up to 60% inhibition. The concentration of inhibitor in normal plasma was 41.5 ± 8.4 units/ml. Inhibitor was detectable in the sera of 9 of 13 patients with hereditary angioneurotic edema at concentrations of 2% to 12% of normal. Spontaneous hydrolysis of the substrate occurred in two patients, and the enzyme responsible was identified as C1̄.Keywords
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