Insulin drug evolution Stage 1 Insulin was extracted from the glands of cows and pigs(1920s) Amino Acid substitutions A-Chain Position B-Chain Position Source/ ypes A8(0A21B2823(B30Ba B32 Ala Val Asn Pro Ly Ala Pork Thr IIc Asn Pro Ala Human Thr llc Asn Pro Lys Thr Stage 2 Convert pig insulin into human insulin by removing the one amino acid that distinguishes them and replacing it with the human versionStage 1 Insulin was extracted from the glands of cows and pigs. (1920s) Stage 2 Convert pig insulin into human insulin by removing the one amino acid that distinguishes them and replacing it with the human version. Insulin drug evolution