Limited proteolysis of human and rabbit immunoglobulins by snake venoms produces Fab-like fragments.

Rabbit and, to a lesser extent, human immunoglobulins (IgGs) are cleaved by snake venoms. The snake venom proteases active on IgGs release fragments which behave on SDS-PAGE like Fab units similar to those released by the thiol-activated enzymes. However, in contrast to the cysteine proteases, the activity of snake venom proteases on IgGs is not only blocked by metal chelating agents but is also inhibited by thiol compounds. The snake enzymes active on IgG are metalloproteases.