CYP4B1 and liver cancer: Next, we evaluated the enzyme activities of the 14 different CYP4B1 orthologs in two experimental set ups: (i) by stable expression of the proteins in two human liver cancer-derived cell lines and analysis of their efficiency of processing the two protoxins 4-IPO and the structurally related perilla ketone (PK), and (ii) by testing the recombinantly expressed CYP4B1 proteins for conversion of lauric acid (LA) and 4-IPO as representative CYP4B1 substrates.