RESUMO
Proteins antigenically related to CoF, the anticomplementary protein of the venom of the Indian hooded cobra (Naja naja), were found in a variety of elapid and viper venoms but not in the venom of Brazilian crotalids . In keeping with this finding was the weak ability of Brazilian snake venom to convert C3 in human serum. All snake serums tested, including Brazilian crotalids , contained a beta-globulin antigenically related to CoF. This serum protein in Brazilian snake serum had a number of characteristics of mammalian C3, including conversion on storage or on incubation of this serum with endotoxin, zymosan or mammalian antigen-antibody precipitates. The serum protein did not, however, convert on incubation with hydrazine. Brazilian crotalid serum did not, as did cobra serum, have the ability to inactivate CoF's ability to activate complement in normal human serum. The crotalid serum had hemolytic activity for rabbit antibody-sensitized and unsensitized sheep red blood cells that was active in the presence of Ca++ and Mg++ or Mg++ alone but greater with Ca++ present, suggesting the presence of both classical and alternative pathways of complement activation. This activity was maximal at 37 degrees C, but was destroyed or inactive after heating at 50 degrees C for 1 hr, incubation with hydrazine or by addition of EDTA. A marked reduction of hemolytic activity of Bothrops serum occurred after removal of the CoF-like protein. These findings suggest that Brazilian snake venom has little CoF-like material, but its serum contains a CoF-like protein with many characteristics of C3.(ABSTRACT TRUNCATED AT 250 WORDS)