BINDING OF 7-DEHYDROCHOLESTEROL TO STEROL CARRIER PROTEIN AND VITAMIN D₃ EFFECT

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It was confirmed that Δ5, 7-sterol Δ7-reductase activity was suppressed by cholecalciferol (vitamin D₃) in the enzyme system consisted of microsomes and sterol carrier protein (SCP).
The enzyme activity was significantly decreased in the combination with microsomes obtained from either vitamin D-deficient or vitamin D₃-treated rat liver and with SCP obtained from vitamin D₃-treated rat. It was also demonstrated by the binding assay of the dextran-charcoal technique that 7-dehydrocholesterol binding to SCP could be specifically displaced by vitamin D₃. The inhibition of cholecalciferol on 7-dehydro-cholesterol binding to liver SCP was confirmed to be non-competitive inhibition.