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

Abstract

Clr was isolated from human serum by DEAE-cellulose column chromatography in the presence of EDTA. The isolated Clr did not hydrolyze N^a-acetyl-L-arginine methyl ester, unless activated by brief treatment with trypsin [EC 3.4.21.4]. On the column, the Cl esterase inhibitor activity was found to coincide with Clr but not Cls (another subcomponent of the first component). Cl¯ was isolated from the euglobulin fraction of human serum by DEAE-cellulose column chromatography. On Sephadex G-200 column chromatography, Cl¯ was eluted in the void volume, whereas Clr was eluted in a position corresponding to a molecular weight of 140, 000–160, 000. The results indicate that, on activation, Clr 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 DEAE-cellulose column chromatography. The inactivated Cl▹ was found to have a larger molecular weight than Cl▹. Trypsin, which activated Clr to Clr, completely inactivated the Cl esterase inhibitor activity of the Clr fraction. From the above evidence it is concluded that Clr is a complex of Cl esterase inhibitor and Cl▹.