Afaq, S., and J. Iqbal. “Immobilization and Stabilization of Papain on Chelating Sepharose: A Metal Chelate Regenerable Carrier”. Electronic Journal of Biotechnology, vol. 4, no. 3, Dec. 2001, pp. 0-0, https://preprints.pucv.cl/index.php/ejbiotechnology/article/view/v4n3-1.