C1r, subunit of the first complement component: purification, properties, and assay based on its linking role


A method to obtain C1r, a subunit of the first complement component, in a highly purified state has been described for the first time. The stepwise method starts with a neutral euglobulin precipitation, after diethylaminoethyl- and carboxymethyl-cellulose chromatography and a final preparative polyacrylamide electrophoresis step. Such C1r preparations are devoid of C1q and C1s activities and show only one protein band on analytic polyacrylamide electrophoresis. Rabbits injected with this preparation produced antisera showing only one precipitation band. The stability of C1r activity was determined under different conditions, and C1r was found to be labile at 37°C, pH 7-8 and low ionic strength.

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