Abstract
Fast acting sterols observed by Liebermann reaction, which mainly contain Δ7-sterol analogue, 7-dehydrocholesterol, were significantly increased 3 hours after an oral administration of vitamin D3 in the vitamin D deficient rat liver.
The decrease of Δ5, 7-sterol-Δ7-reductase [E.C. 1.14.1] activity was also observed by vitamin D3 treatment. While NADPH level was not affected, NADP+ level was decreased by vitamin D3 administration. Using gel filtration technique it was demonstrated that 7-dehydrocholesterol-3H bound to an activator protein of Δ5, 7-sterol-Δ7-reductase both in vivo and in vitro and that this binding of 7-dehydrocholesterol-3H was suppressed by vitamin D3. Vitamin D3-3H was also bound to the activator protein.
From these results, it was shown that vitamin D3 inhibited the conversion of 7-dehydrocholesterol to cholesterol. And the decrease in the binding of 7-dehydrocholesterol-3H to an activator protein by vitamin D3 will suggest that vitamin D3 binds to the activator protein in place of 7-dehydrocholesterol.
