The fourth complement component (C4) of carp Cyprinus carpio was partially purified from serum by affinity chromatography on Blue-Cellulofine, ion-exchange chromatography on DEAE-Toyopearl 650M and gel filtration on Sepharose CL-6B using ammonia-inactivated carp serum as a reagent for detecting C4. About 1, 000-fold purification was achieved in a yield of 25% of the initial hemolytic activity. This partially purified C4 was free of C1 and C2, and it contained trace amounts of C3. The molecular weight of carp C4 was estimated to be 170, 000 by gel filtration on Sepharose CL-6B. The protein migrated to a slow β-globulin region on agarose gel electrophoresis. Carp C4 was stable on heating at 58°C for 60 min. Incubation with ammonia or hydrazine led to inactivation of the component, while carrageenan or zymosan had no effect. These characteristics of carp C4 were in fair agreement with those reported for mammalian C4. Carp C4 was, however, incompatible with C1 or C2 of the guinea pig complement.
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