Some Properties of an Esterase Derived From Preparations of the First Component of Complement

Abstract

Several years ago, an hypothesis was proposed that the first of the four recognized components of complement was the precursor of an enzyme (1).This view was based in part upon observations of the effect of proteolytic enzymes upon human complement. Streptokinase is an activator of plasmin, a proteolytic enzyme of plasma most effective at neutrality. The complement activity of human serum was inhibited by the addition of streptokinase (2). Analysis demonstrated that this loss of complement activity was primarily the result of inactivation of the first, second, and fourth components of complement. However, the inactivation of the second and fourth components occurred only in serums containing the first component (1). These experiments suggested that the streptokinase had activated plasmin which in turn had converted the first component of complement into an agent which inhibited the activity of the second and fourth components.The possibility that the first component of human complement might be a proenzyme has found support in two separate lines of study. In the first group of experiments, it was observed that under certain conditions a partially purified preparation of the first component rapidly lost its hemolytic activity. In its stead, the preparation acquired the capacity to inactivate complement and to hydrolyze certain synthetic amino acid esters (3~ 4). In the second group of experiments, aggregates of antigen and antibody were mixed with fresh human serum. This procedure resulted in a demonstrable loss from the serum of activity attributable to the first component. It was then possible to elute from the aggregates of antigen and antibody one or more factors which inactivated complement and hydrolyzed the same amino acid esters as the preparations derived from the partially purified first component (3, 5). These observations suggested that the first component of complement may have been the precursor of an enzyme tentatively identified as an esterase (3-5). The inhibition of the hemolytic action of guinea pig complement by diisopropyl fluorophosphate, an *

Studies on the Action of Hageman Factor: Evidence That Activated Hageman Factor in Turn Activates Plasma Thromboplastin Antecedent*

“…The esterase activity of crude Hageman factor and of PTA activated by Hageman factor was tested upon a substrate of 0.02 M p-toluenesulfonyl-L-arginine methyl ester for 24 hours at 370 C, using a previously published method (27). The concentration of Hageman factor in the enzyme-substrate mixture was one-tenth that of the plasma from which it was separated.…”

Studies on Immune Cellular Injury

“…Activity and solubility were unimpaired by storage for at least 1 month. One unit of C'I esterase is defined as that amount of enzyme which will liberate 0.5 micromol of fitratable acid during incubation for 15 minutes at 37 ° with N-acetyl-L-tyrosine ethyl ester under standardized conditions of assay (6,7). The preparation of Cq esterase used contained 30 #g. of nitrogen per unit of enzyme.…”

“…Human and various other serums contain a naturally occurring inhibitor, a heat-labile a2-globulin, which can block, under appropriate conditions, both the esterolytic and complement-interacting properties of Cq esterase (6)(7)(8)(9). The inhibitor, partially purified from human serum by ammonium sulfate fractionation and column chromatography, contains only small amounts of serum trypsin and plasmin inhibitors (8).…”

THE INHIBITION OF PLASMIN, PLASMA KALLIKREIN, PLASMA PERMEABILITY FACTOR, AND THE C'1r SUBCOMPONENT OF THE FIRST COMPONENT OF COMPLEMENT BY SERUM C'1 ESTERASE INHIBITOR

“…When C'1 esterase inhibitor was added after kinins had been allowed to generate, it was without effect. DISCUSSION C~1 esterase inhibitor was first detected in human serum by its capacity to inhibit the esterolytic properties of C'1 esterase, an agent derived from the Ct'ls fragment of the first component of complement (1). When partially purified preparations of C'1 esterase inhibitor became available, it became apparent that it also inhibited chymotrypsin (4), plasma kaUikrein, and the permeability-enhancing enzyme in human plasma known as PF/Dil (7,8).…”