Bid BH3 (80-99) is a biologically active peptide and a pro-apoptotic member of the 'BH3-only' (BOPS) subset within the BCL-2 protein family, crucial in apoptosis regulation. It interacts with Bcl-2, Bax, and Bak to initiate their activation or inactivation, inducing cell death. Bid translocates from the cytosol to the mitochondrial membrane as part of its mechanism. Pyroglutamyl (pGlu) peptides, which can arise from Glutamine (Q) or Glutamic acid (E) at the N-terminus, have a hydrophobic γ-lactam ring that enhances stability and provides resistance to gastrointestinal proteases. These peptides are recognized variants in peptide analyses, including HPLC purity assessments.