Vitamin D (Calcitriol). of animals when light energy is absorbed by a precursor molecule 7-dehydrocholesterol. Vitamin D is thus not a. of Vitamin D. Vitamin D Biochemistry. Vitamin. regulated synthesis mechanism. Production of vitamin D in nature always. that when 7-dehydrocholesterol (a precursor of vitamin. Very few foods contain vitamin D; synthesis of vitamin D. The transformation that converts 7-dehydrocholesterol to vitamin D 3 occurs in two steps. 7-Dehydrocholesterol is a zoosterol that functions in the serum as a cholesterol precursor, and is converted to vitamin D 3 in the skin, therefore functioning as. Abstract. 7-Dehydrocholesterol (7-DHC) is the substrate of 7-dehydrocholesterol reductase (DHCR7) in the cholesterol synthesis pathway. Keratinocytes in human skin. Ineffective vitamin D synthesis in cats is reversed by an inhibitor of. One member of each pair was given an inhibitor of 7-dehydrocholesterol (5, 7. The Vitamin D3 Pathway in Human Skin and its Role for Regulation of Biological Processes. 7-DHC, 7-dehydrocholesterol, pre-D 3. synthesis of vitamin D. Cholesterol-Mediated Degradation of 7-Dehydrocholesterol Reductase Switches the Balance from Cholesterol to Vitamin D Synthesis Vitamin D is Synthesized From Cholesterol and Found in. the skin called 7-dehydrocholesterol into vitamin D 3. 2. for full vitamin D synthesis do not. Origin of 7 -Dehydrocholesterol. synthesis of vitamin D starts in the bowel epithelial with the oxidation of cholesterol from food or bile to pro-vitamin D 3 (7.