Flow cytometric analysis of pro-apoptotic proteins expressed by KG-1A cell line. Cells were induced for apoptosis after overnight incubation in medium deprived of serum. For flow cytometric analysis of bak, bad, and bax expression in KG-1A cells, cells were permeabilized with Ortho Permeafix and stained with goat anti-bak, mouse anti-bad, and rabbit anti-bax antibodies followed by staining with FITC-conjugated antigoat, antimouse, and antirabbit IgG antibodies, respectively. For neutralization, the anti-bak antibody (goat polyclonal) was incubated overnight at 4°C with excess peptide antigen. Cells were stained with the peptide/antibody mixture followed by staining with FITC-conjugated antigoat IgG. (A) bax, bak, and bad expression before induction of apoptosis. Only bad protein was expressed by the majority of KG-1A cells. (B) Considerable increase in bax and bak expression following induction of apoptosis. (C) The effect of bak- blocking peptide (PEP) on bak expression in apoptotic cells. Bak expression reduced from 78% before to 11% after neutralization with bak peptide.