Bcl-x(L) does not inhibit the function of Apaf-1

Abstract

Bcl-2 and its relative, Bcl-x(L), inhibit apoptotic cell death primarily by controlling the activation of caspase proteases. Previous reports have suggested at least two distinct mechanisms: Bcl-2 and Bcl-x(L) may inhibit either the formation of the cytochrome c/Apaf-1/caspase-9 apoptosome complex (by preventing cytochrome c release from mitochondria) or the function of this apoptosome (through a direct interaction of Bcl-2 or Bcl-x(L) with Apaf-1). To evaluate this latter possibility, we added recombinant Bcl-x(L) protein to cell-free apoptotic systems derived from Jurkat cells and Xenopus eggs. At low concentrations (50 nM), Bcl-x(L) was able to block the release of cytochrome c from mitoc..