STUDIES ON THE ACTIVATION OF A SERUM ESTERASE WITH ETHER AND ITS RELATIONSHIP TO C′1-ESTERASE*

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Abstract
Serum extracted with ether as described provides a fraction, insoluble in the cold, which is rich in esterase activity ("ether-esterase"). The nature of this esterase suggests its identity with the esterase derived from the first component of complement ("C''1-esterase"). Both C''1-esterase and ether-esterase inactivate the fourth component of complement, hydrolyze the same spectrum of synthetic substrates, and are inhibited by the same fraction of normal serum. Neither may be prepared from serum lacking the first component of complement. They behave in comparable fashion in the presence of antigen-antibody aggregates. Activation of this esterase is apparently auto-catalytic following destruction of its serum inhibitor by ether. Plasmin does not participate in its activation. These observations support the hypothesis that the first component of complement exists as a pro-esterase.