Differences in the metabolism of vitamin D2 and vitamin D3 by subcellular fractions from rat liver

The 25-hydroxylation of vitamin D2 and vitamin D3 was studied in the mitochondrial fraction from rat liver and in a reconstituted system containing cytochrome P-450 from rat liver microsomes. The mitochondrial fraction catalyzed the 25-hydroxylation of vitamin D3 at least two times more effectively than the 25-hydroxylation of vitamin D2. Microsomal cytochrome P-450 catalyzed an efficient 25-hydroxylation of vitamin D3, but no 25-hydroxylation of vitamin D2 could be detected. The present results show a difference in the 25-hydroxylation of vitamin D2 and vitamin D3 in rat liver in vitro.