The Role of Cl Esterase Inhibitor in the Activation of Clr, a Subcomponent of the First Component of Complement from Human Plasma

Abstract

C1r was isolated from human serum by DEAE-cellulose column chromatography in the presence of EDTA. The isolated C1r did not hydrolyze N^α-acetyl-L-arginine methyl ester, unless activated by brief treatment with trypsin [EC 3. 4. 21. 4]. On the column, the C1 esterase inhibitor activity was found to coincide with Clr but not C1s (another subcomponent of the first component).
Cl_??_ was isolated from the euglobulin fraction of human serum by DEAF-cellulose column chromatography. On Sephadex G-200 column chromatography, C1r was eluted in the void volume, whereas C1_??_ was eluted in a position corresponding to a molecular weight of 140, 000-160, 000. The results indicate that, on activation, C1r was converted to an enzyme of lower molecular weight.
Cl_??_ was converted to inactivated Cl_??_ by addition of pseudoglobulin and the latter was isolated by DEAF-cellulose column chromatography. The inactivated C1_??_ was found to have a larger molecular weight than C1_??_.
Trypsin, which activated Clr to C1_??_, completely inactivated the C1 esterase inhibitor activity of the C1r fraction.
From the above evidence it is concluded that C1r is a complex of C1 esterase inhibitor and C1_??_.