Figure 2.

Human insulin molecule with its two polypeptide chains (A and B). The two interchain disulfide bonds (A7–B7, A20–B19) and one intrachain disulfide bond (A6–A11) are also shown. The darkened residues remain conserved across all the species. In porcine insulin, alanine replaces threonine (B30), whereas in bovine insulin, in addition to the substitution in porcine insulin, two additional substitutions are noted: alanine for threonine (A8) and valine for isoleucine (A10). The residues that help dimerization and hexamerization are marked with “D” and “H”, respectively.