Corrigall, A. V., J. A. H. Campbell, K. Siziba, R. E. Kirsch, and P. N. Meissner. “The Expression of Protoporphyrinogen Oxidase IN HUMAN TISSUES”. Cellular and Molecular Biology, vol. 55, no. 2, July 2009, pp. 89-95, https://www.cellmolbiol.org/index.php/CMB/article/view/1092.