Redox enzyme cytochrome P450 3A4, molecular model. Cytochrome P450 is superfamily of enzymes that catalyse bio-oxidation reactions. This example is cytochrome P450 3A4, a vital and versatile enzyme. Among other things, 3A4 oxidizes foreign molecules such as pharmaceuticals, toxins, steroids and carcinogens. Like all cytochromes, 3A4 is a heme protein. The heme group is shown here in red, with its catalytic iron atom in yellow.