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. 2023 Apr 5;62:102695. doi: 10.1016/j.redox.2023.102695

Fig. 1.

Fig. 1

Synthesis of vitamin D3and vitamin D2. 7-dehydrocholesterol is the second last metabolite of the cholesterol biosynthesis pathway, which also reacts into vitamin D3, when it is exposed to UV-B (top left). In plants, vitamin D2 is synthesized based on ergosterol (top right). The liver enzymes CYP2R1 and CYP27A1 convert both vitamin D3 and vitamin D2 into 25(OH)D3 and 25(OH)D2, respectively (bottom). In the kidneys, CYP27B1 adds a hydroxy group to C1 of both molecules resulting in the nuclear hormones 1,25(OH)2D3 and 1,25(OH)2D2, which both activate the transcription factor VDR.