Keefer, LM., Piron, MA., & De Meyts, P. (1981). Human Insulin Prepared By Recombinant Dna Techniques and Native Human Insulin Interact Identically With Insulin-receptors. National Academy of Sciences. Proceedings, 78(3), 1391-1395. https://doi.org/10.1073/pnas.78.3.1391 (Original work published 1981)