Translations:Vitamin D/101/en
Difference between substrates
Vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) share a similar mechanism of action as outlined above. Metabolites produced by vitamin D2 are named with an er- or ergo- prefix to differentiate them from the D3-based counterparts (sometimes with a chole- prefix).
- Metabolites produced from vitamin D2 tend to bind less well to the vitamin D-binding protein.
- Vitamin D3 can alternatively be hydroxylated to calcifediol by sterol 27-hydroxylase (CYP27A1), but vitamin D2 cannot.
- Ergocalciferol can be directly hydroxylated at position 24 by CYP27A1. This hydroxylation also leads to a greater degree of inactivation: the activity of calcitriol decreases to 60% of original after 24-hydroxylation, whereas ercalcitriol undergoes a 10-fold decrease in activity on conversion to ercalcitetrol.