Al-Soufi, Mohammed. A. “Characterization of Purified Polyphenol Oxidase (PPO) from (Lactuca Serriola L.) Prickly Lettuce”. Journal of Biotechnology Research Center, vol. 5, no. 1, Jan. 2011, pp. 40-50, doi:10.24126/jobrc.2011.5.1.144.