They are rate-limiting enzymes that degrade heme into same moles of dehydrobilirubin(biliverdin),CO and Fe.

• 血红素氧合酶催化血红素降解为同摩尔的一氧化碳、胆绿素和铁,胆绿素在胆绿素还原酶作用下,迅速生成胆红素。