Biosyntéza rostlinného vitamínu D

Ergosterol

• Přichází do organismu potravou
• Společně s lipidy je v lumen tenkého střeva emulgován působením žlučových solí (Wilczek 1978, 24)
• V játrech je hydroxylován na metabolit zvaný 25–hydroxyergokalciferol [6]
• Conversion to previtamin D2 by photolysis
• Isomerizes to vitamin D2
• In methanol has a rate comparable to that of previtamin D3
• Process is faster in white button mushrooms [11]

Ergokalciferol

• Rostlinný
• Converted to 25-hydroxyergocalciferol [10]
• Vitamin D3 can alternatively be hydroxylated to calcifediol by sterol 27-hydroxylase (CYP27A1), but Vitamin D2 can not.
• Can be directly hydroxylated at position 24
• Inactivation also tends to have a more profound effect
• Calcitriol's activity decreases to 60% of original after 24-hydroxylation
• Ercalcitriol suffers a 10-fold decrease in activity on conversion to ercalcitetrol [11]
• The researchers Laura Armas, Bruce Hollis, and Robert Heaney showed in 2004
• Vitamin D2's low affinity for the vitamin D-binding protein
• Cca 10x less effective at raising long-term vitamin D levels
• More likely to result in toxicity than is vitamin D3
• Dr. John Cannel, president of the Vitamin D Council: nearly all cases of toxicity from pharmacological doses were by vitamin D2 [17]

25–hydroxyergokalciferol - 25-hydroxyvitamin D - 25(OH)D

• Oproti 25–hydroxycholekalciferolu je jeho účinek
• Menší
• I biologicky méně významnější (Wilczek 1978, 32) [4]

1 alpha,25-Dihydroxyergocalciferol - ercalcitriol

• Vitamin D2 product