Purification of the sixth and seventh component of human complement without loss of hemolytic activity

Procedures for the isolation of the human complement proteins C6 and C7 have been described. These procedures allow isolation of the two proteins without any loss of hemolytic activity. Apparent activity gains of 160% and 140% were observed for C6 and C7, respectively, when the activity of the isolated proteins was compared with their activity in serum. The recovery of C6 was 3.5 to 11% and that of C7 was 7 to 13% of the amount present in serum. C6 has a m.w.of 128,000 and an electrophoretic mobility at pH 8.6 of -2.6 times 10(-5) cm2 s-1 v-1. C7 has a m.w. of 121,000 and an identical electrophoretic mobility. With 3 times 10(7) assay cells, 63% hemolysis was achieved with 1 ng of C6 and 3.8 ng C7. On polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and after reduction with mercaptoethanol, C6 and C7 behaved as single polypeptide chain proteins.