H-Lys-Ala-Glu-Arg-Ala-Asp-Leu-Ile-Ala-Tyr-Leu-Lys-Gln-Ala-Thr-Ala-Lys-OH The I-Ek-restricted T cell response to Cytochrome c - pigeon (pcyt c) is specific for a peptide within the COOH-terminal sequence 88-1041. The minimal length of the pcyt c peptide required for T cell stimulation is the COOH-terminal sequence containing residues 95-104. However, the addition of residues to the NH2 terminus of residue 95 increases the antigenic potency of the peptide; the maximal response is induced by pcyt c 88-1042. The substitution of any residue between 95 and 104 of the cytochrome c peptide changed the antigenic potency of the peptide for at least one of the hybridomas3.