Location and range of disulfide bonds in proteins. (A) In the human antibody κ C_L domain (PDB code: 2R8S), its single internal disulfide bond is located in the hydrophobic core and connects ∼60% of the residues (marked in blue). The cysteine that will covalently link the Ig light chain to the Ig heavy chain in order to form an antibody molecule is shown unpaired at the top of this model. (B) In the Aspergillus oryzae RNase T₁ (PDB code: 3RNT), disulfide bond 1 connects ∼10% of its residues (marked in blue), whereas disulfide bond 2 links ∼90% of its residues (marked in green). Cysteines are shown in a CPK representation with the sulfur atoms highlighted in yellow.