Mechanism of 25-hydroxyvitamin D₃ 24-hydroxylation: incorporation of oxygen-18 into the 24 position of 25-hydroxyvitamin D₃

Abstract

The oxygen enzymatically inserted as a hydroxyl function by chick kidney homogenate into the 24 position of 25-hydroxyvitamin D3 to give 24,25-dihydroxyvitamin D3 is derived exclusively from 18O2. Therefore, like the 25-hydroxyvitamin D3-lalpha-hydroxylase system, the 25-hydroxyvitamin D3-24-hydroxylase system is also a monooxygenase ("mixed-function oxidase").