ABSTRACT
Insulin is a protein consisting of two chains that are designated and , having 21 and 30 amino acids, respectively, and are connected by two disulfide bridges (see Part D). Differences in amino acid sequences between species are small; for example, cattle, sheep, horses, dogs, and whales differ only in positions 8, 9, and 10 of the -chain. Consequently, biologic activities of insulin are not highly species specific. Porcine insulin differs from human insulin by one amino acid (Ala instead of Thr at the carboxy terminal of the - chain), and bovine insulin differs by three amino acids (Ala instead of Thr at -8 as well as the -30 position, and Val instead of Ile at -10). Porcine and bovine insulin have been used for many years to treat insulin-dependent humans. They are still used in dogs and cats, but insulin produced in bacteria via recombinant DNA technology is becoming more widely accepted in human medicine to avoid antibody formation.
