A new method is described for the radiolabeling of C3, C5, and C5a. Using a methylation procedure we have labeled C3, C5, and C5a with 14CH2O, achieving high specific activity, without loss of hemolytic activity in the case of C3 and C5, and in the case of C5a, full retention of chemotactic and enzyme releasing activities. The distribution of radiolabel in the α and β chains of C5 was 75 and 25%, respectively. Using intact labeled C5 the fragmentation pattern in zymosan-activated human serum, assessed by gel filtration and electrophoresis, is complex, yielding multiple fragmentation products. The labeling method described in this paper yield materials that have many advantages over the currently used labeling procedures.
This work was supported by National Institutes of Health Grants HL 25015, HL 22437, HL 23192, AI-09651, AM 25216, and AI-09648.